Recording medium having a substrate containing microscopic pattern of parallel groove and land sections and recording/reproducing equipment therefor

ABSTRACT

An information recording medium  1  at least comprises a substrate  13  having a microscopic pattern  20,  which is constituted by a shape of continuous substance of approximately parallel grooves formed with a groove section G and a land section L alternately, a recording layer  12  formed on the microscopic pattern  20  and a light transmission layer  11  formed on the recording layer. The microscopic pattern  20  is formed so as to satisfy a relation of P&lt;λ&lt;NA and a thickness of the light transmission layer  11  is within a range of 0.07 to 0.12 mm, wherein P is a pitch of the groove section G or the land section L, λ is a wavelength of reproducing light beam and NA is a numerical aperture of an objective lens. Further, there provided an information recording medium, which is improved in cross erase and recorded in high density, and a reproducing apparatus and a recording apparatus for the information recording medium.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending application Ser. No.10/028,978, filed on Dec. 28, 2001, and for which priority is claimedunder 35 U.S.C. § 120; and this application claims priority ofApplication No. 2000-400668 filed in Japan on Dec. 28, 2000; ApplicationNo. 2000-400667 filed in Japan on Dec. 28, 2000; and Application No.2001-290997 filed in Japan on Sep. 25, 2001, under 35 U.S.C. § 119; theentire contents of all are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an information recording medium, areproducing apparatus and a recording apparatus, which reads outinformation from the information recording medium which moves, andparticularly relates to an information recording medium to be recordedand/or reproduced through an optical device, and a reproducing apparatusand a recording apparatus for such an information recording medium.

2. Description of the Related Art

Until now, there is existed a system for reading out information from aninformation recording medium, which moves. In such a system,reproduction is performed by using a device such as an optical device, amagnetic device and a capacitive device. A system, which records and/orreproduces by an optical device, is used extensively in daily living.With respect to a read only information recording medium to bereproduced by using a light beam having a wavelength λ of 650 nm, forexample, mediums such as a DVD (Digital Versatile Disc) Videoprerecorded with video information, a DVD-ROM (Digital VersatileDisc-Read Only Memory) prerecorded with a program or like, and a DVDAudio disc and an SACD (Super Audio Compact Disc) prerecorded withmusical information are well known.

Further, there is provided a DVD-R (Digital Versatile Disk-Recordable)as a recordable recording and reproducing type information recordingmedium, which uses dye. Furthermore, there is provided a DVD-RAM(Digital Versatile Disc-Random Access Memory), a DVD-RW (DigitalVersatile Disk-ReWritable) and a DVD+RW (Digital VersatileDisk+ReWritable) as a recording and reproducing type informationrecording medium, which use phase change. Moreover, there is provided anASMO (Advanced Storage Magneto-Optical) disc, an iD (intelligent image)disc and a GIGAMO (GIGA-byte Magneto-Optical) disc as a recording andreproducing type information recording medium using photo-magnetism.

On the other hand, in order to increase recording density of aninformation recording medium, a study for shortening a wavelength oflaser beam has been continued for a long period of time. A secondharmonic generating element invented recently and a semiconductor lightemitting element composed of gallium nitride system compound (disclosedin the Japanese Patent No. 2778405, for example), emit light having awavelength λ of approximately 350 to 450 nm. Consequently, theseelements can become an important light emitting element, which increasesa recording density sharply.

In addition thereto, design for an objective lens coping with such awavelength has been advanced, particularly, a lens having a numericalaperture (NA) of more than 0.7, which exceeds the NA 0.6 utilized for aDVD disc, is currently developed.

As mentioned above, a reproducing apparatus for an information recordingmedium having capability such that a wavelength λ is shortened to 350 to450 nm and an NA is more than 0.7 has been developing. It is expectedthat an optical disc system, which has a higher recording densityextremely exceeding that of a current DVD disc, can be developed byusing these techniques.

By using such a light beam having a shorter wavelength than one for aDVD disc and a lens having a higher NA, an information recording mediumhaving an extremely higher recording density can be realized. However,coma aberration also increases extremely when an information recordingmedium is slanted. Consequently, an information recording medium ofwhich thickness for light transmission is made extremely thinner thanthat of a DVD disc is required. Actually, a disc system called a “DVRland groove” has been proposed. In the disc system, by using a lightemitting element having a wavelength of 405 nm and an objective lenshaving an NA of 0.85, a thickness of disc for light transmission isdesigned for 0.1 mm.

With referring to FIGS. 1 and 2, a conventional information recordingmedium is explained.

FIG. 1 is a cross sectional view of a conventional information recordingmedium according to the prior art.

FIG. 2 is a fragmentary plan view, partially enlarged, of theconventional information recording medium shown in FIG. 1.

As shown in FIG. 1, an information recording medium 100 is composed of arecording layer 120 and a light transmission layer 110, which arelaminated on a substrate 130 in order. The substrate 130 is formed witha microscopic pattern 200. The recording layer 120 is formed on themicroscopic pattern 200 directly. The microscopic pattern 200 hasmicroscopic patterns composed of land section L1 and L2 (hereinaftergenerically referred to as “land section L”) and groove sections G1through G3 (hereinafter generically referred to as “groove section G”).

While recording, as shown in FIG. 2, a record mark M is formed on boththe land section L and the groove section G (it is called a land-grooverecording method.)

With paying attention to dimensions of the microscopic pattern 200, withdefining that a minimum distance between the centers of adjacent groovesections G is a pitch P (a minimum distance between the centers ofadjacent land sections L is also the pitch P), the land section L andthe groove section G are formed so as to satisfy a relation P>S withrespect to a reproduction spot diameter S of a light beam.

Further, the reproduction spot diameter S can be calculated by anequation S=λ/NA, where λ is a wavelength of a laser beam forreproduction and NA is a numerical aperture of an objective lens. Inother words, the pitch P is designed in order to satisfy a relationP>λ/NA.

In the information recording medium 100, an information recorded in therecording layer 120 is read out by irradiating a reproducing light beamincident on the light transmission layer 110. The information is takenout through the light transmission layer 110 after the reproducing lightbeam has been reflected by the surface of the recording layer 130 andreproduced.

The inventors of the present invention performed an experiment forrecording and reproducing the information recording medium 100 actuallymanufactured by using a light emitting element radiating a light beamhaving a single wavelength within a range of 350 to 450 nm and anobjective lens having a higher NA of 0.75 to 0.9, and then it is foundthat a cross erase phenomenon was remarkable.

The cross erase phenomenon is a phenomenon such that an information tobe recorded in a land section L, for example, is recorded in a groovesection G with overlapping a signal previously recorded in the groovesection G when recording the information in the land section L. In otherwords, it is such a phenomenon that an information previously recordedin a groove section G is erased by recording another information in aland section L.

Further, this phenomenon can also be noticeable in a reverse case. Thatis, the cross erase phenomenon is also recognized if a previouslyrecorded information in a land section L is observed when recording aninformation in a groove section G.

If the cross erase phenomenon occurs, as mentioned above, an informationrecorded in an adjacent track is damaged. In a case of an informationsystem having larger capacity, an amount of lost information becomesexcessively large. Consequently, affection to a user is enormous.Therefore, it is considered for such an information recording medium 100that an information shall be recorded only in either land section L orgroove section G. However, recording capacity of an informationrecording medium will decrease and a merit of the information recordingmedium having a potential of recording in higher density will decline.

SUMMARY OF THE INVENTION

Accordingly, in consideration of the above-mentioned problems of theprior art, an object of the present invention is to provide aninformation recording medium, which is improved in the cross erasephenomenon and recorded in a higher density, and a reproducing apparatusthereof and a recording medium thereof.

Particularly, an object of the present invention is to provide aninformation recording medium with assuming that it is recorded andreproduced by a light beam having a wavelength of 350 to 450 nm and areproducing apparatus and a recording apparatus thereof.

In order to achieve the above object, the present invention provides,according to an aspect thereof, an information recording medium, whichat least comprising: a substrate having a microscopic pattern, which isconstituted by a shape of continuous substance of approximately parallelgrooves formed with a groove section and a land section alternately; arecording layer formed on the microscopic pattern; and a lighttransmission layer formed on the recording layer, the informationrecording layer is characterized in that the microscopic pattern isformed so as to satisfy a relation of P<λ/NA and a thickness of thelight transmission layer is within a range of 0.07 to 0.12 mm, wherein Pis a pitch of the groove section or the land section, λ is a wavelengthof reproducing light beam and NA is a numerical aperture of objectivelens.

According to another aspect of the present invention, there provided areproducing apparatus, which reproduces an information recording mediumat least comprising: a substrate having a microscopic pattern, which isconstituted by a shape of continuous substance of approximately parallelgrooves formed with a groove section and a land section alternately; arecording layer formed on the microscopic pattern; and a lighttransmission layer formed on the recording layer, wherein theinformation recording layer is characterized in that the microscopicpattern is formed so as to satisfy a relation of P<λ/NA and a thicknessof the light transmission layer is within a range of 0.07 to 0.12 mm,and wherein P is a pitch of the groove section or the land section, λ isa wavelength of reproducing light beam and NA is a numerical aperture ofobjective lens, the reproducing apparatus comprising:

a pickup composed of a light emitting element having a wavelength of λwithin a range of 350 to 450 nm and an objective lens having a numericalaperture of NA within a range of 0.75 to 0.9 for reading out reflectedlight from the information recording medium; a motor for rotating theinformation recording medium; a servo device for controlling to drivethe pickup and the motor; a turntable for supporting the informationrecording medium while rotating; a demodulator for demodulating aninformation signal read out by the pickup; an interface (I/F) fortransmitting a signal demodulated by the demodulator externally; and acontroller for controlling the reproducing apparatus totally.

According to further aspect of the present invention, there provided arecording apparatus for recording an original information signal on aninformation recording medium at least comprising: a substrate having amicroscopic pattern, which is constituted by a shape of continuoussubstance of approximately parallel grooves formed with a groove sectionand a land section alternately; a recording layer formed on themicroscopic pattern; and a light transmission layer formed on therecording layer, wherein the information recording layer ischaracterized in that the microscopic pattern is formed so as to satisfya relation of P<λ/NA and a thickness of the light transmission layer iswithin a range of 0.07 to 0.12 mm, and wherein P is a pitch of thegroove section or the land section, λ is a wavelength of reproducinglight beam and NA is a numerical aperture of objective lens, therecording apparatus comprising: a pickup composed of a light emittingelement having a wavelength of λ within a range of 350 to 450 nm and anobjective lens having a numerical aperture of NA within a range of 0.75to 0.9 for reading out reflected light from and recording on theinformation recording medium; a motor for rotating the informationrecording medium; a servo device for controlling to drive the pickup andthe motor; a turntable for supporting the information recording mediumwhile rotating; an interface (I/F) for receiving the originalinformation signal to be recorded; a modulator for modulating theoriginal information signal; a waveform converter for converting theoriginal information signal into a format suitable for a recordingcharacteristic of the recording layer of the information recordingmedium; an auxiliary information demodulator for demodulating adifferential signal outputted from the pickup; and a controller forcontrolling the recording apparatus totally.

Other object and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view of a conventional information recordingmedium according to the prior art.

FIG. 2 is a fragmentary plan view, partially enlarged, of theconventional information recording medium shown in FIG. 1.

FIG. 3 is a cross sectional view of an information recording mediumaccording to a first embodiment of the present invention.

FIG. 4 is a fragmentary plan view, partially enlarged, of theinformation recording medium shown in FIG. 3.

FIG. 5 is a cross sectional view of an information recording mediumaccording to a second embodiment of the present invention.

FIG. 6 is a cross sectional view of an information recording mediumaccording to a third embodiment of the present invention.

FIG. 7 is a cross sectional view of an information recording mediumaccording to a fourth embodiment of the present invention.

FIG. 8 is a cross sectional view in partially enlarged of an informationrecording medium according to a fifth embodiment of the presentinvention.

FIG. 9 is a fragmentary plan view, partially enlarged, of an amplitudemodulation address recorded in an information recording medium accordingto the present invention.

FIG. 10 is a fragmentary plan view, partially enlarged, of a frequencymodulation address recorded in an information recording medium accordingto the present invention.

FIG. 11 is a fragmentary plan view, partially enlarged, of a first phasemodulation address recorded in an information recording medium accordingto the present invention.

FIG. 12 is a fragmentary plan view, partially enlarged, of a secondphase modulation address recorded in an information recording mediumaccording to the present invention.

FIG. 13 is a table exhibiting a change of fundamental data of before andafter a base-band modulation.

FIG. 14 is a table of definite example exhibiting a change of data arrayof before and after a base-band modulation.

FIG. 15 is a block diagram of a first reproducing apparatus according tothe present invention.

FIG. 16 is a graph exhibiting a relation between modulated amplitude anderror rate.

FIG. 17 is a graph exhibiting a relation between a reflectivity and anerror rate.

FIG. 18 is a table showing reflectivity and reproduction characteristicsof embodiments 6 through 12 and comparative examples 4 and 5.

FIG. 19 is a block diagram of a second reproducing apparatus accordingto the present invention.

FIG. 20 is a block diagram of a recording apparatus according to thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

With referring to FIGS. 3 and 4, an information recording mediumaccording to a first embodiment of the present invention will beexplained.

FIG. 3 is a cross sectional view of an information recording mediumaccording to a first embodiment of the present invention.

FIG. 4 is a fragmentary plan view, partially enlarged, of theinformation recording medium shown in FIG. 3.

In FIG. 3, an information recording medium 1 is at least composed of arecording layer 12 and a light transmission layer 11, which are formedand laminated on a substrate 13 formed with a rugged microscopic pattern20 in order. Ruggedness of the microscopic pattern 20 is almost in ashape of continuous substance of parallel grooves G1 through G5(hereinafter generically referred to as groove section G), wherein aplurality of land L1 through L4 (hereinafter generically referred to asland section L) is provided between the groove sections G.

The information recording medium 1 is a read only type medium, which canbe reproduced by using an apparatus composed of a light emitting elementradiating a light beam having a single wavelength within a range of 350to 450 nm and an objective lens having an NA of 0.75 to 0.9. Further, ashape of the information recording medium 1 can be applicable to anyshape such as a disc, a card and a strip or tape. Furthermore, it isalso applicable to a circular, square or oval shape. Moreover, a holecan be provided thereon.

In FIG. 4, “M” is a record mark formed on each of the land section L1through L4 (hereinafter referred to as land section L generically) whilerecording. “P” is a pitch distance between the centers of groovesections G2 and G3 (hereinafter referred to as groove section Ggenerically). “S” is a spot diameter of reproducing light beam(reproduction spot diameter).

In the following paragraphs, the substrate 13, the recording layer 12and the light transmission layer 11 will be detailed.

The substrate 13 is a base having a function of mechanically holding therecording layer 12 and the light transmission layer 11 formed thereon.With respect to a material of the substrate 13, any one of syntheticresin, ceramic and metal can be used.

Typical examples of the synthetic resin are as follows: polycarbonate,polymethyle methacrylate, polystyrene, copolymer of polycarbonate andpolystyrene, polyvinyl chloride, alicyclic polyolefin, variousthermoplastic and thermosetting resins such as polymethyle pentene andvarious energy ray curable resins (including examples of ultraviolet(UV) ray curable resins, visible light curable resins and electron beamcurable resins). They can be used suitably. Further, these materials canbe applicable to be combined with metal powder or ceramic powder.

Further, typical examples of ceramics are as follows: soda lime glass,soda aluminosilicate glass, borosilicate glass and silica glass.Furthermore, a metal plate such as aluminum having no ability for lighttransmission can be used as a typical example of metal.

In order to support other layers mechanically, thickness of thesubstrate 13 is 0.3 to 3 mm, preferably 0.5 to 2 mm. In a case that theinformation recording medium 1 is shaped in disc, it is most desirableto be designed such that a total thickness including the substrate 13,the recording layer 12 and the light transmission layer 11 becomes 1.2mm so as to be interchangeable with conventional optical discs.

The recording layer 12 is a thin film layer having a function of readingout information, recording information or rewriting information. In therecording layer 12, information is recorded in either one section of theland section L and the groove section G. A material, which generates achange of reflectivity, a change of refractive index or both of them, isutilized for the recording layer 12. With respect to a material for therecording layer 12, there is provided a phase change material, whichgenerates a change of reflectivity or change of refractive index or bothchanges between amorphous and crystal by thermal recording, or a dyematerial.

There is provided phase change materials such as Ge—Sb—Te system,Ag—In—Sb—Te system, Cu—Al—Sb—Te system and Ag—Al—Sb—Te system. Theserecording materials can contain one or more elements as an additiveelement within a range of more than 0.01 atomic % and less than 10atomic % in total. Such an additive element is selected out of Cu, Ba,Co, Cr, Ni, Pt, Si, Sr, Au, Cd, Li, Mo, Mn, Zn, Fe, Pb, Na, Cs, Ga, Pd,Bi, Sn, Ti, V, Ge, Se, S, As, Tl and In.

With respect to compositions of each element, for example, there isexisted Ge₂Sb₂Te₅, Ge₁Sb₂Te₄, Ge₈Sb₆₉Te₂₃, Ge₈Sb₇₄Te₁₈, Ge₅Sb₇₁Te₂₄,Ge₅Sb₇₆Te₁₉, Ge₁₀Sb₆₈Te₂₂ and Ge₁₀Sb₇₂Te₁₈ and a system adding a metalsuch as Sn and In to the Ge—Sb—Te system as for the Ge—Sb—Te system.Further, as for the Ag—In—Sb—Te system, there is existed Ag₄In₄Sb₆₆Te₂₆,Ag₄In₄Sb₆₄Te₂₈, Ag₂In₆Sb₆₄Te₂₈, Ag₃In₅Sb₆₄Te₂₈, Ag₂In₆Sb₆₆Te₂₆, and asystem adding a metal or semiconductor such as Cu, Fe and Ge to theAg—In—Sb—Te system.

With respect to a dye material, porphyrin dye, cyanine dye,phthalocyanine pigment, naphthalocyanine pigment, azo dye,naphthoquinone dye, fulgide dye, polymethine dye and acridine dye can beused.

Furthermore, with respect to a material for the recording layer 12, amagneto-optical material, which is reproduced by a change of Kerrrotation angle, can also be used. More accurately, alloys composed of anelement such as terbium, cobalt, iron, gadolinium, chromium, neodymium,dysprosium, bismuth, palladium, samarium, holmium, praseodymium,manganese, titanium, erbium, ytterbium, lutetium and tin are used,(wherein an alloy includes a compound such as oxide, nitride, carbide,sulfide and fluoride). Particularly, constituting an alloy of atransition metal, which is represented by TbFeCo, GdFeCo and DyFeCo,with rare earth element is preferable. Moreover, the recording layer 12can be constituted by using an alternate lamination layer of cobalt andplatinum.

With respect to a forming method of these phase change material, dyematerial and magneto-optical material, such methods as vacuum depositionof resister heating type or electron beam type, direct currentsputtering, high frequency sputtering, reactive sputtering, ion beamsputtering, ion plating and chemical vapor deposition (CVD) can be used.Further, with respect to a material out of dye materials, particularly,a material solvable by solvent, a liquid phase film forming method suchas dip coating, spin coating, bar coating, knife coating and rollcoating can be used.

The light transmission layer 11 has a function of transmitting aconverged reproducing light to the recording layer 12 in a condition ofless optical distortion (the reproducing light is shown by an arrow inFIG. 3). For example, by using a reproducing light having a wavelengthλ, a material having a light transmittance of more than 70% with respectto the reproducing light having the wavelength λ, preferably more than80% can be utilized suitably. It is necessary for the light transmissionlayer 11 to be less optical anisotropy. With considering to controlreduction of reproducing light, actually, a material having abirefringence of less than ±100 nm, preferably ±50 nm, more preferably±30 nm by 90-degree (vertical) incident double paths is used.

Materials having such a characteristic such as polycarbonate,polymethyle methacrylate, cellulose triacetate, polystyrene, copolymerof polycarbonate and polystyrene, polyvinyl chloride, alicyclicpolyolefin and polymethyle pentene an be used the light transmissionlayer 11.

Further, it can be applicable to the light transmission layer 11 thatthe light transmission layer 11 has a function of protecting therecording layer 12 mechanically and chemically. With respect tomaterials having such a function, a material having higher stiffnesssuch as, for example, transparent ceramics (such as soda lime glass,soda aluminosilicate glass, borosilicate glass and silica glass),thermosetting plastics and energy ray curable resins (such as UV raycurable resins, visible light curable resins and electron beam curableresins) can be suitably used.

Furthermore, a thickness of the light transmission layer 11 is desiredto be less than 0.120 mm from a point of view that coma aberration canbe suppressed when the information recording medium 1 is slanted withrespect to a reproducing light beam or recording light beam. More, fromanother point of view of preventing the recording layer 12 from ascratch, it is desired to be more than 0.07 mm. In other words, thethickness is desired to be within a range of 0.070 to 0.120 mm. If amaterial of the light transmission layer 11 is one of the materialsmentioned above, an index “z” of refraction is 1.45 to 1.7. Therefore,in a case of considering optical factors, a range of ideal thickness ofthe light transmission layer 11 is 0.093 to 0.107 mm.

Moreover, scattering of thickness in one plane shall be ±0.003 mm at themaximum, desirably less than ±0.002 mm. More desirably, it must be lessthan ±0.001 mm.

With referring to FIG. 4, the microscopic pattern 20, which is one ofthe features of the present invention, is explained next.

As mentioned above, microscopically, the microscopic pattern 20 iscomposed of a continuous substance of almost parallel grooves. On theother hand, macroscopically, it can be formed in any shape such as line,coaxial and spiral.

As shown in FIG. 4, in the microscopic pattern 20, a raised portion isthe land section L and a sunken portion is the groove section G, whereinthey are arranged alternately in parallel with each other.

The groove section G follows the definition of the Table 4.4-1 listed inthe text “Understanding Optical Disc by this” (edited by the JapanPatent Office, published in 2000 by Japan Institute of Invention andInnovation). That is to say, in a disc, the groove section G is “asunken groove, which is previously provided spirally or coaxially inorder to form a recording track on a surface of substrate”. Further, theland section L also follows the definition in the same text. That is, ina disc, the land section L is “a raised portion, which is previouslyprovided spirally or coaxially in order to form a recording track on asurface of substrate”, wherein the substrate is equivalent to thesubstrate 13 of the present invention.

If it is defined that a minimum distance between the centers of adjacentgroove sections G is the pitch P (a minimum distance between the centersof adjacent land sections L is also the pitch P), the land section L andthe groove section G are formed so as to satisfy a relation P<S withrespect to the reproduction spot diameter S of a light beam, wherein thereproduction spot diameter S is calculated by a equation S=λ/NA, where λis a wavelength of a laser beam for reproduction and NA is a numericalaperture of an objective lens. In other words, the pitch P satisfies arelation P<λ/NA. For example, the pitch P is set to be within a range of250 to 600 nm. If it is considered that a HDTV (High DefinitionTelevision) picture is recorded for a period of two hours approximately,the pitch P is desirable to be within a range of 250 to 450 nm.

An appropriate depth of the groove G is within a range of 10 to 300 nm,particularly, with considering a wavelength λ of a reproduction opticalsystem, the depth is suitable within a range of λ/(8z) to λ/(18z),wherein “z” is an index of refraction of the light transmission layer 11at the wavelength λ. In a case of considering that λ=405 nm and z=1.6(polycarbonate), for example, a most suitable range of the depth iswithin a range of 14 to 32 nm.

Microscopically, one groove section G and the other groove section G,one land section L and the other land section G, and the groove sectionG and the land section L are in parallel to each other respectively.However, in order to embed an analog or digital auxiliary informationsuch as clock and address, these sections can be wobbled very little.

For example, it is acceptable that these grooves are recorded with asingle frequency so as to embed clock, and consequently wobbledsinusoidally on the surface of the substrate 13. In order to embed anauxiliary information (sub information) such as address, these groovescan be modulated in amplitude modulation (AM), frequency modulation (FM)or phase modulation (PM) and wobbled in various patterns.

In other words, at least either one of an area recorded with a singlefrequency for clock and a modulation recording area for embeddingaddress can be formed in either the groove section G or the land sectionL. A modulation method for embedding the auxiliary information (subinformation) such as address will be detailed.

In a case that the information recording medium 1 is shaped in disc, thewobbling mentioned above can be recorded by the CAV (Constant AngularVelocity) method or the CLV (Constant Linear Velocity) method. Further,with forming zones varying by radius, the ZCAV (Zone Constant AngularVelocity) method or the ZCLV (Zone Constant Linear Velocity) method ofwhich controlling varies by each zone can also be adopted.

Furthermore, although it is not shown, the groove section G or the landsection L is cut in pieces over a certain area in order to embed anauxiliary information such as address, an inherent pit can be formed.More, by allocating an inherent pit in the groove section G adjacent tothe land section L, or by allocating the inherent pit in the landsection L in adjacent to the groove section G, an auxiliary informationsuch as address can be embedded. Moreover, a hologram or a visiblemicroscopic pattern for identifying the information recording medium 1can be formed in an area other than a recording area.

In the information recording medium 1, an information recorded in therecording layer 12 is read out by irradiating a reproducing light beamincident on the light transmission layer 11. The information is takenout through the light transmission layer 11 after the reproducing lightbeam has been reflected by the surface of the recording layer 13 andreproduced.

The surface itself of the recording layer 12 of the informationrecording medium 1 has a certain degree of reflectivity, so that areproduction can be functioned by the recording layer 12 as it is.However, in order to improve a reflectivity of a reproducing light beamand to add other functions such as increasing a number of rewritings andimproving weather resistance, a reflective layer or a protective layercan be provided in adjacent to the recording layer 12. In additionthereto, materials for the reflective layer and the protective layerwill be detailed.

Cross erase of the information recording medium 1 of the presentinvention is evaluated in comparison with that of the conventionalinformation recording medium 100.

The configuration of the information recording mediums 1 and 100 aresuch that the substrates 13 and 130 are polycarbonate resin, therecording layers 12 and 120 are AgInSbTe one of phase change materialsand the light transmission layers 11 and 110 are polycarbonate resin.

Evaluation is performed as follows: recording a second track andreproducing, recording first and third tracks with a frequency otherthan that of recorded in the second track 10 times, and then measuringan output of the second track once again.

As a result of the evaluation, by the conventional information recordingmedium 100, cross ease of −5 dB in maximum is observed. However, by theinformation recording medium 1 of the present invention, cross ease of−2 dB in maximum is observed. That is to say, in the conventionalinformation recording medium 100, an output reduces by 5 dB incomparison with an output of the second track if the first and thirdtracks are not recorded. On the contrary, an output of the informationrecording medium 1 of the present invention reduces by only 2 dB.

In other words, by using the information recording medium 1 according tothe present invention, cross erase is improved by 3 dB in comparisonwith the conventional information recording medium 100.

According to an aspect of the first embodiment of the present invention,as mentioned above, with defining that a pitch between two adjacentgroove sections G or land sections L is “P”, a wavelength of laser beamis “λ” and a numerical aperture of objective lens is “NA”, aninformation recording medium is constituted such that a microscopicpattern 20 having a relation of “P<λ/N” is formed and either the landsection L or groove section G is recorded. Accordingly, an informationrecording medium, which is recorded in high density in conjunction withenabling to reduce cross erase, can be obtained.

Second Embodiment

With referring to FIG. 5, an information recording medium according to asecond embodiment of the present invention is explained.

FIG. 5 is a cross sectional view of an information recording mediumaccording to a second embodiment of the present invention.

In FIG. 5, same compositions as those of the first embodiment shown inFIG. 3 are indicated by the same sign as that of the first embodimentrespectively and their explanations are omitted.

As shown in FIG. 5, an information recording medium 2 is the sameconfiguration as that of the first embodiment except for the lighttransmission layer 11. A light transmission layer of the secondembodiment is composed of a light transmission layer 11 a and anadhesive light transmission layer 11 b.

The light transmission layer 11 a is identical to the light transmissionlayer 11 of the first embodiment. On the contrary, the adhesive lighttransmission layer 11 b is a layer for adhering the light transmissionlayer 11 a to the recording layer 12 firmly and an adhesive resin havinga light transmittance of more than 70%, desirably more than 80% for alight beam having a wavelength λ . Such an adhesive resin is as follows:thermosetting resin, various energy ray curable resin (such as UV raycurable resin, visible light curable resin and electron beam curableresin), moisture curable resin, plural liquid mixture curable resin andthermoplastic resin containing solvent.

A thickness of the adhesive light transmission layer 11 b is desirableto be more than 0.001 mm as a minimum thickness for exhibiting adhesionand less than 0.04 mm in consideration of preventing an adhesivematerial from stress crack, more desirable to be within a range of morethan 0.001 mm and less than 0.03 mm. The most desirable thickness iswithin a range of more than 0.001 mm and less than 0.02 mm. However, inconsideration of warp of the total information recording medium 2, thethickness is most desirable to be within a range of more than 0.001 mmand less than 0.01 mm.

With respect to a coating method of the light transmission layer 11 a,such a method as spin coat, splay, dip, blade coat, roll coat, knifecoating, screen printing and offset printing can be used.

The information recording medium 2 of the second embodiment is evaluatedfor cross erase by the same manner as that of the first embodiment andan identical result with the first embodiment is obtained.

Consequently, an identical effect with the information recording medium1 according to the first embodiment can be obtained by the informationrecording medium 2 according to the second embodiment of the presentinvention.

Third Embodiment

With referring to FIG. 6, an information recording medium according to athird embodiment of the present invention is explained.

FIG. 6 is a cross sectional view of an information recording mediumaccording to a third embodiment of the present invention.

In FIG. 6, same compositions as those of the first embodiment shown inFIG. 3 are indicated by the same sign as that of the first embodimentrespectively and their explanations are omitted.

As shown in FIG. 6, an information recording medium 3 is the sameconfiguration as that of the first embodiment except for a resin layer14 formed with a microscopic pattern 21. The information recordingmedium 3 is composed of the resin layer 14 formed with the microscopicpattern 21, a recording layer 12 and a light transmission layer 11,which are laminated on a substrate 13 a in order.

In the information recording medium 3 according to the third embodimentof the present invention, forming the microscopic pattern 21 on theresin layer 14 is different from the first embodiment of which themicroscopic pattern 20 is formed on the surface of the substrate 13.

A material for the resin layer 14 is as follows: thermosetting resin,various energy ray curable resin (such as UV ray curable resin, visiblelight curable resin and electron beam curable resin), moisture curableresin, plural liquid mixture curable resin and thermoplastic resincontaining solvent. A light beam for reproducing or recording does notreach as far as the resin layer 14, so that there is no restriction fora transmittance of material of the resin layer 14. With respect to athickness of the resin layer 14, it is desirable to be less than 0.02 mmin consideration of warp of the information recording medium 3 in total.

The information recording medium 3 of the third embodiment is evaluatedfor cross erase by the same manner as that of the first embodiment andan identical result with the first embodiment is obtained.

Consequently, an identical effect with the information recording medium1 according to the first embodiment can be obtained by the informationrecording medium 3 according to the third embodiment of the presentinvention.

Fourth Embodiment

With referring to FIG. 7, an information recording medium according to afourth embodiment of the present invention is explained.

FIG. 7 is a cross sectional view of an information recording mediumaccording to a fourth embodiment of the present invention.

In FIG. 7, a same composition as that of the first embodiment shown inFIG. 3 is indicated by a same sign as that of the first embodiment andits explanation is omitted.

As shown in FIG. 7, an information recording medium 4 is composed of apattern transferring layer 15 having a microscopic pattern 22, arecording layer 12, an adhesive light transmission layer 11 a and alight transmission layer 11 b, which are laminated on a substrate 13 bin order.

Further, in the information recording medium 4 according to the fourthembodiment of the present invention, it is different from the secondembodiment that the top surface of the substrate 13 b being in contactwith the pattern transferring layer 15 is flat, and that the microscopicpattern 22 is formed on the pattern transferring layer 15 adjoining tothe substrate 13 b.

The pattern transferring layer 15 is an extremely thin film so as tohave the microscopic pattern 22. With respect to a material for thepattern transferring layer 15, it is selected out of a metal, its alloy(including composition such as oxide, nitride, carbide, sulfide andfluoride), and resin. Further, thickness of the material is chosen froma range of 5 nm to 0.020 mm approximately. A typical example of resin issuch as novolac photosensitive resin and polyhydroxy styrenephotosensitive resin, which can be developed by alkali.

The information recording medium 4 of the fourth embodiment is evaluatedfor cross erase by the same manner as that of the first embodiment andan identical result with the first embodiment is obtained.

Consequently, an identical effect with the information recording medium1 according to the first embodiment can be obtained by the informationrecording medium 4 according to the fourth embodiment of the presentinvention.

It is apparent that each component of the information recording mediums1 through 4 shown in FIGS. 3 through 7 respectively can be replaced witheach other or combined as far as a reproduction characteristic is notdeteriorated. For example, by preparing two mediums out of theinformation recording mediums 1 through 4, they can be adhered togetherwith facing each substrate 13, 13 a or 13 b (hereinafter genericallyreferred to as “substrate 13”) towards each other. Further, another setof the recording layer 12 and the light transmission layer 11 or 11 a(hereinafter generically referred to as “light transmission layer 11”)can be laminated on the light transmission layer 11 of the informationrecording mediums 1 through 4. By constituting as mentioned above, arecording capacity of the information recording medium 1 through 4 canbe increased approximately twice.

Furthermore, although not shown in any drawings, an antistatic layercommonly known can be formed on the surface of light transmission layer11 opposite to the recording layer 12 in order to decrease dust adheringto the surface of the light transmission layer 11.

A hard coat layer or a lubricative layer (either one is not shown) canbe formed on the surface of the light transmission layer 11 opposite tothe recording layer 12 for a purpose of reducing an affection caused byan accidental collision of an objective lens, which constitutes a pickupof reproduction apparatus such as shown in FIG. 15, with the lighttransmission layer 11.

With respect to a material for such a hard coat layer, an actualmaterial having a light transparency of more than 70% for a light beamhaving a wavelength λ is as follows: thermosetting resin, various energyray curable resin (such as UV ray curable resin, visible light curableresin and electron beam curable resin), moisture curable resin, pluralliquid mixture curable resin and solvent containing thermoplastic resin.

The hard coat layer is desirable to exceed a certain value of the“scratch test by pencil” regulated by the Japanese Industrial Standard(JIS) K5400 in consideration of abrasion resistance of the lighttransmission layer 11. In consideration of that a hardest material ofthe objective lens is glass, a value of the “scratch test by pencil” forthe hard coat layer is most preferable to be more than the “H” grade. Ifthe test value is less than the “H” grade, dust caused by scraping thehard coat layer is remarkably generated. Consequently, an error rate isdeteriorated abruptly.

Further, a thickness of the hard coat layer is desirable to be more than0.001 mm in consideration of shock resistance, more desirable to be lessthan 0.01 mm in consideration of warp of an information recording mediumin total. With respect to a coating method of the hard coat layer, sucha method as spin coat, splay, dip, blade coat, roll coat, knife coating,screen printing and offset printing can be used.

With respect to other materials for the hard coat layer, an elementhaving a light transparency of more than 70% for a light beam having awavelength λ and having a value of the “scratch test by pencil” of morethan the “H” grade such as carbon, molybdenum and silicon, and theiralloy (including composition such as oxide, nitride, carbide, sulfideand fluoride) can be used (its film thickness is within a range of 1 to1000 nm). With respect to a forming method of the hard coat layer, suchmethods as vacuum deposition of resister heating type or electron beamtype, direct current sputtering, high frequency sputtering, reactivesputtering, ion beam sputtering, ion plating and chemical vapordeposition (CVD) can be used.

With respect to an actual material for the lubricative layer, lubricantof which surface energy is adjusted by modifying hydrocarbonmacromolecule with silicon and fluorine can be used. Further, athickness of the lubricative layer is desirable to be within a range of0.01 to 10 nm approximately. With respect to a coating method of thelubricative layer, such a method as spin coat, splay, dip, blade coat,roll coat, knife coating, screen printing and offset printing can beused.

A label printing can be performed on the surface of the substrate 13although not shown in any drawings. Various energy ray curable resinscontaining pigment and dye (such as UV ray curable resin, visible lightcurable resin and electron beam curable resin) can be used suitably forthe label printing. A thickness of the label printing is preferable tobe more than 0.001 mm in consideration of visibility of the printing,more preferable to be less than 0.05 mm in consideration of warp of theinformation recording mediums 1 through 4 in total. With respect to aprinting method, such a method as screen printing and offset printingcan be used.

In order to improve easier loading of the information recording mediums1 through 4 into a reproducing apparatus and protectiveness based onhandling them, a constitution containing the information recordingmedium in a cartridge can be considered.

Further, in a case that the information recording mediums 1 through 4are in a disc shape, its dimensions are not limited. Various sizes, forexample, 20 to 400 mm in diameter can be acceptable, in any diametersuch as 32, 41, 51, 60, 65, 80, 88, 120, 130, 200, 300 and 356 can alsobe acceptable.

In order to improve a recording characteristic and reproductioncharacteristic, the recording layer 12 can be composed of a plurality ofthin film materials. Such a recording layer composed of a plurality ofthin film materials will be detailed in the following embodiment.

Fifth Embodiment

With referring to FIG. 8, an information recording medium of whichrecording layer is composed of four layers of thin film materialsaccording to a fifth embodiment of the present invention is explained.

FIG. 8 is a cross sectional view in partially enlarged of an informationrecording medium according to a fifth embodiment of the presentinvention.

In FIG. 8, a same composition as that of the first embodiment shown inFIG. 3 is indicated by a same sign as that of the first embodiment andits explanation is omitted.

As shown in FIG. 8, an information recording medium 5 is composed of areflective layer 121, a first protective layer 122, a recording layer123, a second reflective layer 124 and a light transmission layer 11,which are laminated on a substrate 13 having a microscopic pattern 20 inorder.

With respect to a material of the reflective layer 121, there isprovided a metal having a light reflectiveness such as Al, Au and Ag, analloy containing the metal as a main component and an additive elementsuch as more than one kind of metal or semiconductor and a mixture of ametal such as Al, Au and Ag with a metal compound such as metal nitride,metal oxide and metal chalcogenide. A metal such as Al, Au and Ag and analloy containing the metal as a main component are high inreflectiveness and thermal conductivity. Therefore, such a metal andalloy are preferable to be used.

Further, the reflective layer 121 has a role of optimizing thermalconduction while recording onto the recording layer 123. Therefore, itcan be called a heat sink layer.

With respect to the alloy mentioned above, there is provided an alloy ofadding at least one element out of Si, Mg, Cu, Pd, Ti, Cr, Hf, Ta, Nb,Mn, Zr and Rh as an additive element to Al or Ag within a range of morethan 1 atomic % and less than 5 atomic % in total or another alloy ofadding at least one element out of Cr, Ag, Cu, Pd, Pt and Ni to Auwithin a range of more than 1 atomic % and less than 20 atomic %.Particularly, the reflective layer 121 is desirable to be constituted byany of Al—Cr alloy, Al—Ti alloy, Al—Ta alloy, Al—Zr alloy, Al—Ti—Cralloy or Al—Si—Mn alloy, which contains Al as a main component and anadditive element controlled within a range of more than 0.5 atomic % andnot more than 3 atomic % in total, because they are excellent incorrosion resistance and improve repetition ability.

With respect to an additive element, adding a metal or a semiconductoris more preferable than a metal alone, because a crystalline particlebecomes smaller and a noise level decreases when reproducing. Further,adding an additive is better so as to improve stability in an ambienceof high temperature and high humidity.

Such an additive is an alloy such as Al—Ti, Al—Cr, Al—Zr, Al—Si,Ag—Pd—Cu and Ag—Rh—Cu. In a case of using a blue semiconductor laserhaving a wavelength of approximately 400 nm, using an alloy such asAl-system and Ag-system can obtain higher reflectivity. With respect toa thickness of the reflective layer 121, it is more than 10 nm and lessthan 300 nm.

The film thickness of the reflective layer 121 varies by a thermalconductivity of a metal or an alloy constituting the reflective layer121. In a case of an Al—Cr alloy, for example, thermal conductivitydecreases in response to increasing content of Cr. Therefore, it doesnot conform to a recording strategy unless the film thickness ofreflective layer 121 is thickened. In a case of increasing content ofCr, the recording layer 123 becomes easy to be heated and hard to becooled, that is so called, to be a gradually cooling structure. In orderto control forming a record mark by the recording strategy, some ideasuch as shortening a head pulse, shortening multi-pulse or extending acooling pulse is required.

If a thickness of the reflective layer 121 exceeds 50 nm, the reflectivelayer 121 does not change optically and does not affect a value ofreflectivity. However, affection to a cooling speed becomes larger.Since it takes more time to manufacture the thicker reflection layer 121having a thickness of more than 300 nm, the film thickness of reflectionlayer 121 must be controlled, if possible, by using a material having ahigher thermal conductivity.

If the reflective layer 121 is divided into two layers or more, a noiselevel can be reduced when reproducing the information recording medium5. Such a recording layer is formed, for example, as follows:

By using a single disc sputtering system, which forms each film on eachlayer in a plurality of vacuum chambers, in a case of forming thereflective layer 121 having a thickness of 150 nm in total bytransporting the substrate 13 one by one, a first reflective layer isformed in a first vacuum chamber at a filming speed of 2 nm/s, and thensecond and third reflective layers are formed by second and third vacuumchambers respectively at a filming speed of 6.5 nm/s. Consequently,discs can be filmed one after another in a short period of time as longas 10 seconds. A crystalline particle can be made finer by changing afilming speed, so that a noise level can be reduced when reproducing theinformation recording medium 5.

The first protective layer 122 and the second protective layer 124 havean effect of protecting the substrate 13 and the recording layer 123from excessive heat, preventing the substrate 13 and the recording layer123 from deformation by the heat and preventing a recordingcharacteristic from being deteriorated. Consequently, the first andsecond protective layers 122 and 124 have an effect of improving asignal contrast by an optical interference effect while reproducing.

These protective layers 122 and 124 are transparent at a wavelength of alight beam for recording and reproducing and its refractive index “n” iswithin a range of 1.9≦n≦2.5.

The first protective layer 122 and the second protective layer 124 arenot required to be a same material and composition. It is acceptable tobe constituted by different materials. A thickness of the secondprotective layer 122 decides a wavelength exhibiting a minimum value ofspectral reflectance.

Further, the first protective layer 122 and the second protective layer124 have a further effect of activating crystallization of a recordinglayer and increasing an erase ratio. With respect to a material of thesefirst and second protective layers 122 and 124, there is existed aninorganic thin film such as ZnS, SiO₂, silicon nitride and aluminiumoxide.

Particularly, a thin film of oxidized metal or semiconductor such as Si,Ge, Al, Ti, Zr and Ta, a thin film of nitride metal or semiconductorsuch as Si, Ge and Al, a thin film of carbide metal or semiconductorsuch as Ti, Zr, Hf and Si, a thin film of sulfide metal or semiconductorsuch as ZnS, In₂S₃, TaS₄ and GeS₂ and a film of a mixture containingmore than two compounds out of the above-mentioned compounds such asoxide, nitride, carbide and sulfide are desirable for the first andsecond protective layers 122 and 124 because they are high in heatresistance and chemically stable.

Furthermore, with respect to a material of the first and secondprotective layers 122 and 124, it is desirable that the material doesnot diffuse into the recording layer 121. These compounds of oxide,sulfide, nitride and carbide are not necessary to be a stoichiometricalcomposition. Controlling a composition and using them by mixing are alsoeffective for controlling a refractive index. By changing a contentamount of oxygen, sulfur, nitrogen and carbon, a refractive index “n” iscontrolled. If a content amount of them increases, a refractive indexdecreases.

A mixture film of ZnS and SiO₂ is particularly desirable for a materialof the first and second protective layers 122 and 124, because recordingsensitivity and C/N (carrier to noise ratio) are barely deteriorated byrepetitions recording and reproducing. A thickness of the firstprotective layer 122 and the second protective layer 124 are within arange of 10 to 500 nm respectively. The thickness of the firstprotective layer 122 is desirable to be within a range of 10 to 50 nm soas to be excellent in a recording characteristic such as C/N and eraseratio and to be rewritable stably a plurality of times.

If a thickness of the first protective layer 122 is thinner, areflectivity increases and a recording sensitivity decreases. Further, aspace between the first protective layer 122 and the reflective layer121 becomes narrower and the first protective layer 122 becomes a rapidcooling construction, so that a relatively large recording power isnecessary to forming a record mark. On the contrary, if the thickness offirst protective layer 122 becomes thicker, the space between the firstprotective layer 122 and the reflective layer 121 becomes wider and thefirst protective layer 122 becomes a gradually cooling structure.Consequently, a rewriting performance is deteriorated and a repetitionnumber of overwriting decreases.

A film thickness of the first protective layer 122 is thinner than thatof the second protective layer 124, the first protective layer 122becomes a rapid cooling structure. In order to relieve thermal damage, afilm thickness of the first protective layer 122 is desirable to bewithin a range of 2 to 50 nm. Further, it is preferable that a filmingspeed of the first protective layer 122 must be slower than that of thesecond protective layer 124. Consequently, increasing of jitter byrewriting is suppressed and a number of rewriting increases.

With respect to a material of the recording layer 123, the same phasechange material as that of the recording layer 12 of the first throughfourth embodiment can be used. A film thickness of the recording layer123 is within a range of 5 to 100 nm, desirably, 10 to 30 nm in order toincrease a reproduced signal.

The same material as the first protective layer 122 is used for thesecond protective layer 124. A thickness of the second protective layer124 is within a range of 10 to 200 nm. The thickness of the secondprotective layer 124 is desirable to be within a range of 40 to 150 nmin order to increase a reproduced signal although an optimum filmthickness varies by a wavelength of a light source to be used. In a casethat a laser beam for recording is blue (having a wavelength of 400 nmapproximately), a modulated amplitude can be increased if the filmthickness of the second protective layer 124 is set to be 40 to 60 nm.

As mentioned above, according to an aspect of the fifth embodiment ofthe present invention, recording and reproducing characteristics of theinformation recording medium 5 can be improved in addition to theeffects according to the first through fourth embodiment.

The laminated structure of the protection layers can be applied to theinformation recording mediums 2 though 4 as well as the informationrecording medium 1. Further, in order to improve the recording andreproducing characteristics more, an auxiliary thin film can be formedon each layer or between layers.

As mentioned above, according to the first through fifth embodiment ofthe present invention, recording in either the groove section G or theland section L can decrease the cross erase.

Furthermore, for a point of view of signal quality, the informationrecording medium 5 of the present invention is studied that either ofthe groove section G and the land section L is more suitable to berecorded. Consequently, it is found that an error rate is low and arewriting characteristic is excellent when recorded in the land sectionL.

In consideration of the allocation of the land section L, which isallocated in a closer side to the light transmission layer 11 than thegroove section G, and a reproduction light, which enters in from thelight transmission layer 11, it is understood that the area of the landsection L has a nature of ideally recording a record mark in a uniformshape as well as can easily accumulate heat in a material of the landsection L and becomes higher sensitivity. (On the other hand, in a caseof recording in the groove section G, heat is easily radiated.Therefore, it is understood that an ideal recording can hardly beperformed.)

A modulation pattern for embedding an auxiliary information (subinformation) such as address data in analog or digital with respect tothe information recording medium 1 according to the present invention isdetailed next.

The auxiliary information (sub information) is recorded in a form ofwobbled pattern by the method of amplitude modulation (AM), frequencymodulation (FM) or phase modulation (PM) as mentioned above. In otherwords, the auxiliary information is directly recorded (on the substrate13 or the light transmission layer 11 and formed in a shape of groove)as a wobbling pattern. Therefore, the auxiliary information is apermanent information being disabled to rewrite.

In a case that the information recording medium 1 is in a disc shape,the auxiliary information is recorded in a wobbling form with respect toa groove, which extends to the tangential direction of the disc.Consequently, the wobbling direction is the radial direction of thedisc.

An address data, which is one of the auxiliary information (subinformation) to be recorded in the present invention, is a date selectedout of an absolute address, which is assigned to whole the informationrecording medium 1, a relative address, which is assigned to a partialarea, a track number, a sector number, a frame number, a field number, atime information and a error correction code. It is a data, which isconverted from a data described in the decimal notation or thehexadecimal notation, for example, to the binary notation (including theBCD code and gray code).

Further, an auxiliary information other than an address data can also behandled. Such an auxiliary information is a specific code data, which isat least selected out from information and data such as, for example, atype of information recording medium, a size of the informationrecording medium, an ideal recording capacity of the informationrecording medium, an ideal linear recording density of the informationrecording medium, an ideal linear velocity of the information recordingmedium, a track pitch of the information recording medium, a recordingstrategy information, a reproducing power information, a manufacturerinformation, a manufacturing number, a lot number, a control number, acopyright related information, a key for producing a cipher, adeciphering key, a ciphered data, a recording permission code, arecording refusal code, a reproduction permission code and areproduction refusal code. It is also acceptable that these data areaccompanied by an error correction code.

In order to simplify explanation, hereinafter it is explained withassuming that an auxiliary information (sub information) is an address.

FIG. 9 is an enlarged plan view of an address 250 recorded by theamplitude modulation (AM) method in an information recording mediumaccording to the present invention. The address 250 is recorded in shapepartially or totally onto either the groove section G or the landsection L, which constitutes the microscopic pattern 20. In the AMmethod, a data “1” or “0” is recorded in accordance with an amplitudewhether or not it is existed. In a case of FIG. 9, a data “1” isrecorded as a section 251 having amplitude and another data “0” asanother section 252 having no amplitude.

In a case that an address “10110”, for example, is recorded, as shown inFIG. 9, the section 251, the other section 252, the section 251, thesection 251 and the other section 252 are sequentially recorded inshape. Such a recording method of data in response to amplitude whetheror not it is existed is advantageous to be able to demodulate even in adeteriorated C/N circumstance because the AM method is a simple signalformat system. Particularly, affection of crosstalk from an adjacenttrack can be minimized. Consequently, the AM method is an effectiveaddress recording method for the information recording medium 1according to the present invention reducing the pitch P more than thespot diameter S of a light beam for reproduction.

Each duration of the section 251 and the other section 252 is acceptableto be either the same duration or not. However, the duration isdesirable to be the same in order to make an error rate of demodulationthe best. Further, a number of waves constituting the section 251 is notlimited to one specific number. The number must be plural in order toeliminate a readout error, and a number being not redundant is suitablefor the number of waves so as not to decrease a recording density ofaddress recording. From the point of view of the above-mentionedcircumstances, the number of waves is desirable to be 2 to 10approximately. Furthermore, each amplitude of a plurality of thesections 251 can be different from each other. However, it is desirableto be the same in consideration of easier setting of a slice level whendemodulating.

In a case that an extra area recorded with a single frequency for clockother than the address 250 is provided, it is not concerned whether ornot the single frequency is the same as a frequency of the section 251.However, if it is the same frequency, a physical length used forextracting clock can be extended slightly. Consequently, the samefrequency is advantageous for stable extraction of clock to be easier.

FIG. 10 is an enlarged plan view of an address 300 recorded in aninformation recording medium according to the present invention by thefrequency modulation (FM) method. The address 300 is recorded in shapepartially or totally onto either the groove section G or the landsection L, which constitutes the microscopic pattern 20. In the FMmethod, a data “1” or “0” is recorded in accordance with a frequencywhether it is higher or lower. In a case of FIG. 10, a data “1” isrecorded as a section 301 having a higher frequency and another data “0”as another section 302 having a lower frequency.

In a case that an address “10110”, for example, is recorded, as shown inFIG. 10, the section 301, the other section 302, the section 301, thesection 301 and the other section 302 are sequentially recorded inshape.

Such a recording method of data in response to a frequency whether it ishigher or lower is advantageous to be able to demodulate by a simplifiedcircuitry. Particularly, as shown in FIG. 10, by selecting a properphase, which is suitable for two waves to be connected continuously at apoint where their frequencies change over, a reproduction envelopebecomes approximately constant and stable address extraction can berealized. Each duration of the section 301 and the other section 302 isacceptable to be either the same duration or not. However, the durationis desirable to be the same in order to make an error rate ofdemodulation the best.

A number of waves constituting the section 301 and the other section 302is arbitrary. Further, each amplitude of the section 301 and the othersection 302 can be different from each other. However, it is desirableto be the same amplitude in consideration of easier demodulation.Furthermore, selecting a frequency of the section 301 and the othersection 302 is arbitrary. However, it is desirable to assign the twofrequencies of which phase difference is within a range of ±π/12 to±π/0.75. Particularly, in a case that a frequency ratio (of higherfrequency to lower frequency) is assigned to be 1.5 as shown in FIG. 10,the two frequencies are related to that a phase of each wave is shiftedby −π/2.5 and +π/2.5 respectively. These two frequencies can beexpressed in integral multiples (triple and twice hereat) of a singlefrequency (0.5 hereat). Consequently, there is existed an advantage ofconstituting a demodulation circuit simply. Moreover, a demodulation canbe performed by the synchronous detection method, so that an error ratecan be reduced remarkably.

In a case that a frequency ratio (of higher frequency to lowerfrequency) is assigned to be 1.28 as another example, the twofrequencies are related to such that a phase of each wave is shifted by−π/4 and +π/4 respectively. Consequently, in this case, a demodulationcan also be performed by the synchronous detection method, so that anerror rate can be reduced remarkably.

In a case that an extra area recorded with a single frequency for clockother than the address 300 is provided, it is acceptable that the singlefrequency and frequencies of the section 301 and the other section 302are different frequencies from each other. However, a physical lengthused for extracting clock can be extended slightly if either frequencyof the section 301 and the other section 302 is the same as that of thesingle frequency. Consequently, the same frequency is advantageous forstable extraction of clock to be easier.

FIG. 11 is an enlarged plan view of a first phase modulation (PM)address 400 recorded in an information recording medium according to thepresent invention. The first PM address 400 is recorded in shapepartially or totally onto either the groove section G or the landsection L, which constitutes the microscopic pattern 20. In the PMmethod, a data “1” or “0” is recorded in accordance with a phasedifference. In the case of FIG. 11, a data “1” is recorded as a “sine 0”section 401 and another data “0” as a “sine π” section 402. Further, ina case that an address “10110”, for example, is recorded, as shown inFIG. 11, the “sine 0” section 401, the “sine π” section 402, the “sine0” section 401, the “sine 0” section 401 and the “sine π” section 402are sequentially recorded in shape.

Such a recording method of data in response to a phase difference isadvantageous to be able to reproduce by demodulating by the synchronousdetection method even in a deteriorated C/N circumstance. Each durationof the “sine 0” section 401 and the “sine π” section 402 is acceptableto be either the same duration or not. However, the duration isdesirable to be the same in order to make an error rate of demodulationthe best. Further, each amplitude of the “sine 0” section 401 and the“sine π” section 402 can be different from each other. However, it isdesirable to be the same amplitude in consideration of easierdemodulation.

Furthermore, a phase difference between two data is assigned to be π andthe two data are recorded in two values of “0” and π. However, it is notlimited to “0” and π. For example, with assigning that a phasedifference is π/2, it is acceptable to be recorded in four values of−3π/4, −π/4, +π/4 and +3 π/4.

In a case that an extra area recorded with a single frequency for clockother than the first PM address 400 is provided, it is acceptable thatthe single frequency and a frequency of either the “sine 0” section 401or the “sine π” section 402 are different from each other. However, aphysical length used for extracting clock can be extended slightly ifthese frequencies coincide with each other. Consequently, the samefrequency is advantageous for stable extraction of clock to be easier.

Further, the single frequency for clock can be recorded by superimposingon the first PM address 400. In other words, an integral multiples(including one) or one over integral multiples of frequency can besuperimposed on a PM address. In a case of superimposing a clockfrequency as mentioned above, frequencies can be separated by using acommonly known band pass filter. However, it is desirable that frequencydifference between the first PM address 400 and a clock frequency islarger. For example, with assuming that a frequency of the first PMaddress 400 is “1” and a clock frequency is ½, these frequencies areideally separated and both address and clock can be extracted stably.

FIG. 12 is an enlarged plan view of a second phase modulation (PM)address 450 recorded by the PM method. A shape is recorded in either thegroove section G or the land section L constituting the microscopicpattern 20. In this method, a wave is regarded as an asymmetrical shapeof rising and falling. Phase difference is expressed by controlling eachwave individually. That is, in a case of FIG. 12, the data “1” isrecorded as a section 451 of which a wave rises gradually and fallsrapidly (hereinafter referred to as a rapidly falling section 451), andthe data “0” as a section 452, which rises rapidly and falls gradually(hereinafter referred to as a rapidly rising section 452).

In a case that an address “10110”, for example, is recorded, as shown inFIG. 12, the rapidly falling section 451, the rapidly rising section452, the rapidly falling section 451, the rapidly falling section 451and the rapidly rising section 452 are sequentially recorded in shape.

Such a recording method of data in response to a phase difference isadvantageous to be able to demodulate by inputting into a wide-bandfilter and extracting a differential component even in a deterioratedC/N circumstance. Each duration of the rapidly falling section 451 andthe rapidly rising section 452 is acceptable to be either the sameduration or not. However, the duration is desirable to be the same inorder to make an error rate of demodulation the best.

Each amplitude of the rapidly falling section 451 and the rapidly risingsection 452 can be different from each other. However, it is desirableto be the same amplitude in consideration of easier demodulation.Further, in a case that an extra area recorded with a single frequencyfor clock other than the second PM address 450 is provided, it isacceptable that the single frequency and a frequency of either therapidly falling section 451 or the rapidly rising section 452 aredifferent from each other. However, a physical length used forextracting clock can be extended slightly if these frequencies coincidewith each other. Consequently, the same frequency is advantageous forstable extraction of clock to be easier.

In the explanation of recording methods by the AM, FM and PM heretofore,it is explained by using the recording method, which records an addressdata itself as a shape of wobbling groove directly. Further, afundamental wave of wobbling groove is on the assumption of a sinusoidalshape. However, the shape according to the present invention is notlimited to the sinusoidal shape. For example, it is apparent that thesame effect is recognized by using a cosine shape for the fundamentalwave of wobbling groove.

An address data can also be recorded in multiple recording and timesharing recording by a different modulation method. For example, it canbe recorded by synthesizing different methods such as AM+FM, AM+PM andFM+PM. Further, it can be recorded by a time sharing recording methodsuch as recording for a period of time by the AM and for another periodof time by the FM, recording for a period of time by the AM and foranother period of time by the PM or recording for a period of time bythe FM and for another period of time by the PM. As mentioned above, itis also acceptable that a single frequency area for extracting a clockis recorded for a certain period of time being different from the periodfor recording the address data as a time sharing recording method inaddition to the time sharing recording of the address data.

With respect to an amplitude of wobbling groove, by assigning adeflection amplitude by wobbling s as to be less than the pitch P,excellent reproduction of address can be realized. Actually, an address,which does not contact with an adjacent track physically, can berecorded by assigning amplitude by wobbling to be less than the pitch P,so that crosstalk caused by recording can be eliminated.

By attempting such that writing a random data by the phase changerecording in a groove, which is recorded with an address with assigningsuch a wobble amplitude to be less than the pitch P, and thenreproducing the address by the push-pull method, it is found that awobble amplitude (peak to peak) is more than 2% of the spot diameter Sof light beam for reproduction as a limit possible to detect the addresssignal. Further, it is found that a random data caused by the phasechange recording is remarkably superimposed as a noise and an addresserror rate increases suddenly with respect to a groove formed such thatthe wobble amplitude is less than 2% of the spot diameter S.

On the other hand, in a case that the wobble amplitude is more than 9%of the spot diameter S, crosstalk from an adjacent track is remarkablysuperimposed on a push-pull signal and an address error rate increasessuddenly. Consequently, a wobble amplitude is essential to be less thanthe pitch P. Further, it is most suitable for the wobble amplitude to bewithin a range of 2 to 9% of the spot diameter S of light beam forreproduction.

In the present invention, the recording method is not limited to thedirect recording. In a case of recording a long array of address data,it is possible that a plurality of “0”s or a plurality of “1”s isarranged sequentially and a direct current component is generated in thedata by the direct recording method.

In order to eliminate such possibility, it is acceptable to perform amethod such that the data is previously modulated by the base-bandmodulation and recorded. In other words, the method is that replace “0”and “1” with another code previously and reduce a sequence of “0”s and“1”s to a certain number or less. With respect to such a method, themethod such as Manchester code, PE (phase encoding) modulation, MFM(modified frequency modulation), M2 (Miller squared) modulation, NRZI(non return to zero inverted) modulation, NRZ (non return to zero)modulation, RZ (return to zero) modulation and differential modulationcan be used alone or by combining some of them.

FIG. 13 is a table exhibiting a change of fundamental data of before andafter a base-band modulation.

With respect to a base-band modulation method, which is most suitablefor the information recording medium 1 of the present invention, it isthe Manchester code (biphase modulation) method. The Manchester codemethod is a method of applying 2 bits to each one bit of data to berecorded as shown in FIG. 13. That is, “00” or “11” is assigned to adata “0” to be recorded, and “01” or “10” to a data “1”. Further, aninverted code of inverting a last code of preceding data is essentiallyapplied to a head code of succeeding data when arranging the succeedingdata after the preceding data.

FIG. 14 is a table of definite example exhibiting a change of data arrayof before and after a base-band modulation. As shown in FIG. 14, anaddress data “100001” is assigned to be a code array of “010011001101”.The original address data contains a sequence of four “0”s. Further, theoriginal address data is an asymmetrical data that an appearingprobability of “0” is twice that of “1”. If such an asymmetrical data ismodulated, a sequence of “0” or “1” is two maximally and the originaldata is converted into a symmetrical data having equal appearingprobability of “0” and “1”. As mentioned above, the base-bandmodulation, which restricts a sequence of same bits within a certainquantity, is effective to increase stability of reading out a data.Consequently, the base-band modulation method is suitable forpre-treatment for a long address data.

Further, there is existed another method of highly analyzing an addressdata and recording it in dispersion. For example, in combination with adummy data “10”, it is a recording method such that an address data isrecorded as a data array of “10X”, wherein “X” is either “0” or “1”, andthe data array is allocated at every certain interval. If the “X” isextracted by using the dummy data “10” as a data trigger, the originaldata can be restored. This method is effective for a format, which canbe read a data array to be treated with taking a long period of time.

With respect to another example of the dispersion recording, there isexisted a method such that a first specific data pattern (“101”, forexample), which is easy to read, is allocated (recorded) at everycertain interval, and then a second specific data pattern (“1111”, forexample), which is easy to read, is allocated between the first specificdata patterns. A position of allocating the second specific pattern isadvanced to a predetermined distance (time) with respect to the firstspecific pattern. The second specific pattern is recorded as a data “1”if the other second specific patter is existed at the position. If theother second specific patter is not existed at the position, a data “0”is recorded there.

When reading a data, with paying attention to a predetermined position,the second specific pattern can be read out whether or not it isexisted. By following such a method, a recorded address data can be readout. Further, by assigning two positions of allocating the secondspecific pattern previously, which are advanced to a predetermineddistance (time) with respect to the first specific pattern, a data “1”or “0” can be recorded at either position, where the second specificpatter exists.

The dispersion recording method by using a difference in distancebetween the first specific pattern and the second specific pattern isexplained above. However, in a case that a pattern having extremely highaccuracy in readout can be provided for a specific pattern, the firstspecific pattern and the second specific pattern are acceptable to beidentical with each other. With respect to a specific pattern recordedby a certain period of time interval, it is acceptable that the data “1”and the data “0” are identified by extracting another specific patternhaving a shorter time interval than the specific pattern and measuringthe time interval.

The recording of an auxiliary information (sub information) composed ofan address information and a specific code data by wobbling groove isexplained hereinbefore. Although it is repeated once again, therecording explained herein is recording in shape by wobbling of a groove(the groove section G or the land section L) not recording onto therecording layer 12. The recording in shape by wobbling groove of theauxiliary information and the clock information (single frequency forextracting clock) mentioned above is a permanent information, which cannot be altered and is high in concealment. Such recording can beperformed by applying a method of forming a record accompanying shapechange on the substrate 13 or the light transmission layer 11.

The forming a record is realized by using a stamper recorded withwobbling groove. The stamper itself is manufactured by the so-calledmastering method for forming a wobbling pattern by using an energy ray.

In the meantime, as mentioned above, recording onto the recording layer12 (phase change recording, for example) is applied to the groovesection G or the land section L. When recording onto the recording layer12, the recording is performed with referring to an auxiliaryinformation and a clock information recorded by wobbling groove (forexample, recording with reading an address). Therefore, a track appliedfor recording must coincide with another track recorded in shape with anauxiliary information and a clock information.

For example, if a track applied for recording is the land section L,another track recorded in shape with the auxiliary information and theclock information must be the land section L. If they are different fromeach other, the auxiliary and clock information are extracted withmixing with 50% each of information recorded in adjacent two tracks, sothat accurate auxiliary information and clock information can not beextracted, although recording onto the recording layer 12 can bephysically performed without any problem.

In another case, if a track applied for recording is the land section Land another track recorded in shape with an auxiliary information and aclock information is the groove section G, recording onto the landsection L in the recording layer 12 is naturally performed. However, ifthe auxiliary information such as an address and the clock informationare extracted while recording, an information recorded in two adjacentgroove sections G, which sandwich the land section L, is read out.Consequently, the auxiliary and clock information are extracted withmixing with 50% each of auxiliary information and clock informationrecorded in two adjacent groove sections G different from the originalgroove section G.

It is impossible to separate the mixed two information, so thatrecording onto a track intended to be recorded can not be performed.Accordingly, a track applied for recording is necessary to coincide withanother track recorded in shape with an auxiliary information and aclock information.

As mentioned above, recording onto the recording layer 12 is suitable torecord on the land section L in a sense of decreasing an error rate.Therefore, it is most desirable that a track supplied for recording isthe land section L and another track recorded in groove shape with anauxiliary information and a clock information is also the land sectionL.

With referring to FIG. 15, a first reproducing apparatus 40 utilized forreproducing the information recording mediums 1 through 5 is explainednext.

FIG. 15 is a block diagram of a first reproducing apparatus according tothe present invention.

In order to simplify an explanation, hereinafter the informationrecording medium 1 represents the information recording mediums 1through 5 generically.

As shown in FIG. 15, a first reproducing apparatus 40 is at leastcomposed of a pickup 50 for reading out reflected light from theinformation recording medium 1, a motor 51 for rotating the informationrecording medium 1, a servo device 52 for controlling to drive thepickup 50 and the motor 51, a turntable 53 for supporting theinformation recording medium 1, a demodulator 54 for demodulating aninformation signal read out by the pickup 50, an interface (I/F) 55 fortransmitting a signal demodulated by the demodulator 54 externally and acontroller 60 for controlling the first reproducing apparatus 40totally. The demodulator 54 is a digital converter, which restores a16-bit data to an original 8-bit data, in a case of the 8/16 modulation(Eight to Fifteen Modulation Plus: EFM Plus) method utilized in the DVDsystem, for example.

The turntable 53 and the information recording medium 1 are connectedwith plugging a center hole Q of the information recording medium 1 withthe turntable 53. Such a connection between the turntable 53 and theinformation recording medium 1 can be either a fixed connection orsemi-fixed connection, which can load or release the informationrecording medium 1 freely. Further, the information recording medium 1can be installed in a cartridge. With respect to a cartridge, a commonlyknown cartridge having an opening and closing mechanism in the centercan be used as it is.

The motor 51 is linked to the turntable 53, supports the informationrecording medium 1 through the turntable 53 and supplies relative motionfor reproduction to the information recording medium 1. A signal outputcan be supplied to a not shown external output terminal or directlysupplied to a not shown display device, audio equipment or printingequipment.

The pickup 50 is further composed of a light emitting element 50 a,which irradiates a light beam having a single wavelength λ within arange of 350 to 450 nm, desirably 400 to 435 nm, an objective lens 50 bhaving a numerical aperture NA within a range of 0.75 to 0.9 and a notshown photo detector, which receives a reflected light reflected by theinformation recording medium 1. Furthermore, the pickup 50 forms areproducing light 70 in conjunction with these components.

It is acceptable that the light emitting element 50 a is a semiconductorlaser of gallium nitride system compound or a laser having a secondharmonic generating element.

The servo device 52 is indicated just one in FIG. 15. However, it can bedivided into two; one is a driving control servo for the pickup 50 andthe other is another driving control servo for the motor 51.

A commonly know equalizer and a PRML (partial response maximumlikelihood) decoding circuit, both are not shown, can be installed inthe demodulator 54. With respect to an equalizer (waveform equalizer),for example, a so-called neural net equalizer (such as disclosed in theJapanese Patent No. 2797035) in which a plurality of conversion systemshaving a nonlinear input-output characteristic is combined together withapplying individual variable weighting and constitutes a neural network,a so-called limit equalizer (such as disclosed in the Japanese PatentApplication Laid-open Publication No. 11-259985/1999) in which anamplitude level of reproduced signal is limited to a predetermined valueand forwarded to a filtering process, and a so-called error selectiontype equalizer (such as disclosed in the Japanese Patent ApplicationLaid-open Publication No. 2001-110146) in which an error between areproduced signal and an objective value for waveform equalization isobtained and a frequency of waveform equalizer is changed adaptively soas to minimize the error can be preferably used.

Further, in the commonly known PRML decoding circuit containing apredicted value controlling and equalization error calculating circuit,a so-called adaptive viterbi decoder (such as disclosed in the JapanesePatent Application Laid-open Publications No. 2000-228064 and No.2001-186027) in which a predicted value utilized for decoding viterbialgorithm is calculated and a frequency response is optimized so as tominimize an equalization error of waveform equalizer can be suitablyused.

Operations of the first reproducing apparatus 40 are explained next.

The reproducing light 70 emitted form the light emitting element 50 a ofthe pickup 50 is converged at the microscopic pattern 20 in theinformation recording medium 1. Actually, the reproducing light 70 isfocused on the microscopic pattern 20, which is allocated at a depth of0.07 to 0.12 mm equivalent to a thickness of the light transmissionlayer 11.

Succeedingly, tracking of the reproducing light 70 is performed toeither one of the groove section G or the land section L. The trackingis performed with choosing a predetermined side. However, as mentionedabove, choosing the land section L is most desirable. A recorded signalis read out by a light detector not shown with receiving a reflectedlight from the microscopic pattern 20.

The light detector is divided into 4 sections. A total sum signal (thatis, Ia+Ib+Ic+Id) of output from all 4 sections of the light detector istransmitted to the demodulator 54, wherein each of Ia, Ib, Ic and Idcorresponds to each output of a 4-division light detector for a DVD discdefined by the JIS Standard No. X6241: 1997. Reading out of the recordedsignal is performed by reproducing the record mark M recorded in thegroove section G or the land section L on the microscopic pattern 20.

It is omitted in the above explanation that a focus error signal isnecessary for focusing to be generated and a tracking error signal isnecessary for tracking to be generated. Such a focus error signal and atracking error signal are generated by a differential signal (that is,“(Ia−Ib)−(Ic−Id)”) of output from a 4-division light detector in theradial direction and transmitted to the servo device 52.

In accordance with control by the controller 60, in the servo device 52,a focus servo signal and a tracking servo signal are generated from thereceived focus error signal and the tracking error signal andtransmitted to the pickup 50. In the meantime, a rotary servo signal isgenerated in the servo device 52 and transmitted to the motor 51.

Further, in the demodulator 54, the recorded signal is demodulated andapplied with error correction according to demand, and an obtained datastream is transmitted to the I/F 55. Finally, a signal is outputtedexternally in accordance with control by the controller 60.

As mentioned above, the information recording medium 1 and the firstreproducing apparatus 40 according to the present invention are designedfor coping with the reproducing light 70, which is produced by the lightemitting element 50 a having single wavelength λ within the range of 350to 450 nm and the objective lens 50 b having the numerical aperture NAof 0.75 to 0.9. Therefore, the first reproducing apparatus canpreferably reproduce the information recording medium 1.

With respect to the light emitting element 50 a in the first reproducingapparatus 40, it is defined that the light emitting element 50 a can bea semiconductor laser of gallium nitride system compound or a laserhaving a second harmonic generating element. However, these twodifferent lasers have a characteristic laser noise respectively,particularly, in a case of a semiconductor laser of gallium nitridesystem compound, it is characterized by a higher noise level.

According to an actual measurement, an RIN (relative intensity noise) ofa laser having a second harmonic generating element is −134 dB/Hz. Thenoise level is almost equivalent to that of a red semiconductor laser(λ=650 nm approximately) utilized for a DVD disc.

On the other hand, in a case of a semiconductor laser of gallium nitridesystem compound, an RIN is −125 dB/Hz. The noise level is larger thanthat of a laser having a second harmonic generating element by 9 dB. Thenoise is added to a reproduced signal from the information recordingmedium 1 and a S/N of the reproduced signal is extremely deteriorated.In other words, if a semiconductor laser of gallium nitride systemcompound is adopted for the first reproducing apparatus 40, a signalcharacteristic is deteriorated. Therefore, it signifies that a designingguide obtained by a DVD disc can not be applied for the firstreproducing apparatus 40 with shifting the designing guideproportionally. Consequently, in a case of the first reproducingapparatus 40 having a semiconductor laser of gallium nitride systemcompound, an information recording medium having a signal characteristicof compensating a deteriorated component is necessary to be provided inconsideration of being added with a noise inherent to a laser.

With respect to the information recording medium 5 shown in FIG. 8according to the fifth embodiment of the present invention, arelationship between modulated amplitude and error rate is examined bymanufacturing various kinds of mediums with varying material andthickness of the reflective layer 121, the first protective layer 122,the recording layer 123 and the second protective layer 124 and byreproducing the mediums by using the first reproducing apparatus 40,which is installed with a semiconductor laser of gallium nitride systemcompound (having a RIN of −125 dB/Hz) for the light emitting element 50a.

In addition thereto, recording on the information recording medium 5 isperformed under a most ideal recording condition, which decreases anerror rate maximally.

Reproduced modulated amplitude is also called an output of reproducedsignal. In a case of a phase change recording material, it is an indexhaving correlation with reflectivity contrast between crystal andamorphous. In more accurately, a modulation signal so-called a (d, k)signal is recorded on the information recording medium 5. A recordingapparatus will be explained later.

A fixed length code and a variable length code can be applied for a (d,k) modulation signal. Such a (d, k) modulation as (2, 10) modulation ina fixed length code, (1, 7) modulation in a fixed length code, (1, 9)modulation in a fixed length code, (2, 7) modulation in variable lengthcode and (1, 7) modulation in the variable length code can be suitablyused.

Examples representing the (2, 10) modulation in a fixed length code arethe 8/15 modulation (such as disclosed in the Japanese PatentApplication Laid-open Publication No. 2000-286709), the 8/16 modulation(EFM plus) and the 8/17 modulation (EFM). Further, an examplerepresenting the (1, 7) modulation in the fixed length code is the “D1,7” modulation (such as disclosed in the Japanese Patent Application No.2001-80205 in the name of Victor company of Japan, Limited).Furthermore, an example representing the (1, 9) modulation in the fixedlength code is the “D4, 6” modulation (such as disclosed in the JapanesePatent Application Laid-open Publication No. 2000-332613). Moreover, anexample representing the (1, 7) modulation in the variable length codeis the 17PP modulation (such as disclosed in the Japanese PatentApplication Laid-open Publication No. 11-346154/1999).

Modulated amplitude is obtained from a signal having a maximal lengthused by a code by reproducing the information recording medium 5 loadedflat (without declining) in the first reproducing apparatus 40 and byconnecting a reproduced signal in the DC system outputted from thepickup 50 to an oscilloscope.

In the case of the 8/16 modulation used for a DVD disc, for example, themaximal length is 14 T. By measuring an I14L and I14H as specified bythe specification (JIS Standard X6241: 1997), modulated amplitude can beobtained by calculating (I14H−I14L)/I14H.

Further, an error rate is obtained by measuring a reproduced signalobtained through the demodulator 54. A result of obtaining modulatedamplitude and an error rate is shown in FIG. 16.

FIG. 16 is a graph exhibiting a relation between modulated amplitude anderror rate.

As shown in FIG. 16, there is existed a definite correlation betweenmodulated amplitude and error rate. It is apparent that an error rateremarkably increases in accordance with decreasing modulated amplitude.By assigning a practical error rate to 3×10⁻⁴ defined by a DVD disc orlike, a necessary modulated amplitude is more than 0.34.

Further, the information recording medium 5 warps by temperature changeor like in circumstances of utilization of the information recordingmedium 5. Therefore, with assuming that a declination of approximate 0.7degree is possible to occur as a same situation as a DVD disc, an errorrate increases due to coma aberration, which is complexly produced by awavelength λ within a range of 350 to 450 nm, an NA within a range of0.75 to 0.9 and a thickness of the light transmission layer 11 within arange of 0.07 to 0.12 mm.

By the result of measurement, it is found that the error rate of 3×10⁻⁴at the declination of 0.7 degree is equivalent to an error rate of0.7×10⁻⁴ at the declination of zero degree. In other words, the errorrate of 0.7×10⁻⁴ is essential in consideration of a possible declinationwhen using the information recording medium 5 practically. Accordingly,it is understood that practical modulated amplitude is more than 0.4.

As mentioned above, in the case that a semiconductor laser of galliumnitride system compound is used for a light emitting element, an errorrate can be reduced to a practical level as low as that of the DVD discspecification if modulated amplitude of the information recording medium5 is assigned to be more than 0.4 in consideration of a noise beingadded to a reproduced signal. Further, it is found by experiments that acorrelation between modulated amplitude and error rate such as shown inFIG. 16 can be obtained as a similar result by applying any of themodulation methods mentioned above.

A maximum mark length can vary by a modulation method. However, a signaloutput almost saturates at more than 6 T by these modulation methods andconverges to a certain value. Consequently, modulated amplitude obtainedby recording the information recording medium 1 by the 17PP modulationmethod, for example, and another modulated amplitude obtained by the8/16 modulation method become a same value as each other. Modulatedamplitude by the (1, 7) system modulation method such as the “D1, 7”modulation method and the 17PP modulation method can be obtained by(I8H−I8L)/I8H because the maximum mark length becomes 8 T.

Hereinafter, information recording mediums according to embodiments 1through 5 are more actually explained. In addition thereto, samples ofinformation recording mediums according to comparative examples 1through 3 are also manufactured in order to compare.

Embodiment 1

Polycarbonate having a thickness of 1.1 mm is used for a substrate 13 ofa phase change type information recording medium 5. Further, theinformation recording medium 5 is manufactured by using materials suchas AgPdCu for a reflective layer 121, ZnSSiO₂ for a first protectivelayer 122, AgInSbTe for a recording layer 123, ZnSSiO₂ for a secondprotective layer 124 and polycarbonate having a thickness of 0.10 mm fora light transmission layer 11. An address data is recorded in a wobblingshape on a land section L of the information recording medium 5 by thefrequency modulation method, wherein a phase having a phase differenceof ±π/2.5 is selected so as for a wave to be continuous at a point ofchanging a frequency. Furthermore, the information recording medium 5 isdesigned with assuming that it is recorded by using a light beam havinga wavelength λ of 405 nm and an objective lens having a numericalaperture NA of 0.85, and a pitch P between land sections L is 0.32 μm.

The information recording medium 5 is loaded into a recording apparatuscomposed of a pickup having a wavelength λ of 405 nm and a numericalaperture NA of 0.85, and a recording signal is recorded on a landsection L by a modulated signal, which is modulated by the 17PPmodulation method, wherein a minimum mark length (equivalent to 2 T) is0.149 μm.

The information recording medium 5 recorded with the above-mentionedrecording signal is loaded into the reproducing apparatus 40 equippedwith the pickup 50 having the wavelength λ of 405 nm and the numericalaperture NA of 0.85 shown in FIG. 15. By reproducing a land section L ofthe information recording medium 5, a signal having modulated amplitude,equivalent to (I8H−I8L)/I8H, of 0.52 can be reproduced. Succeedingly, anerror rate of reproduced signal is obtained and resulted in an excellenterror rate of 2×10⁻⁵. Consequently, a data without any practicalproblems can be extracted. Further, an address error rate is about 1% ata recorded section, so that an address data can be restored excellently.

In addition thereto, if an address error rate is less than 5% whenreproducing after recorded on the recording layer 12, a data includingthe least error can be restored through a process of error correction.Accordingly, the address error rate of about 1% is suitable for theinformation recording medium 5.

Embodiment 2

An information recording medium of an embodiment 2 is identical to thatof the embodiment 1 except for a modulation method for recording arecording signal. The information recording medium of the embodiment 2is recorded with a recording signal modulated by the “D4, 6” modulationmethod, wherein a minimum mark length (equivalent to 2 T) is 0.154 μm,and then reproduced as the same processes as those of the embodiment 1.

By reproducing a land section L of the information recording medium, asignal having modulated amplitude, equivalent to (I12H−I12L)/I12H, of0.60 can be reproduced. Succeedingly, an error rate of reproduced signalis obtained and resulted in an excellent error rate of 8×10⁻⁶.Consequently, a data without any practical problems can be extracted.Further, an address error rate is about 1% at a recorded section, sothat an address data can be restored excellently.

Embodiment 3

An information recording medium of an embodiment 3 is identical to thatof the embodiment 1 except for a modulation method for recording arecording signal. The information recording medium of the embodiment 3is recorded with a recording signal modulated by the “D8-15” modulationmethod, wherein a minimum mark length (equivalent to 3 T) is 0.185 μm,and then reproduced as the same processes as those of the embodiment 1.

By reproducing a land section L of the information recording medium, asignal having modulated amplitude, equivalent to (I12H−I12L)/I12H, of0.63 can be reproduced. Succeedingly, an error rate of reproduced signalis obtained and resulted in an excellent error rate of 4×10⁻⁶.Consequently, a data without any practical problems can be extracted.Further, an address error rate is about 1% at a recorded section, sothat an address data can be restored excellently.

Embodiment 4

An information recording medium 5 of an embodiment 4 is identical tothat of the embodiment 1 except for a modulation method for recording arecording signal. The information recording medium 5 is recorded with anaddress data by the PM method shown in FIG. 10 on a land section L in awobbling shape. The information recording medium 5 is recorded with arecording signal modulated by the 17PP modulation method, wherein aminimum mark length (equivalent to 2 T) is 0.149 μm, and then reproducedas the same processes as those of the embodiment 1.

By reproducing a land section L of the information recording medium, asignal having modulated amplitude, equivalent to (I12H−I12L)/I12H, of0.60 can be reproduced. Succeedingly, an error rate of reproduced signalis obtained and resulted in an excellent error rate of 2×10⁻⁶.Consequently, a data without any practical problems can be extracted.Further, an address error rate is about 0.01% at a recorded section, sothat an address data can be restored excellently.

Embodiment 5

An information recording medium 5 of an embodiment 5 is identical tothat of the embodiment 1 except for a modulation method for recording arecording signal. An address data is recorded in a wobbling shape on aland section L of the information recording medium 5 by the base-bandmodulation method by Manchester code, wherein a phase having a phasedifference of ±π/2.5 is selected so as for a wave to be continuous at apoint of changing a frequency. The information recording medium 5 isrecorded with a recording signal modulated by the “D4, 6” modulationmethod, wherein a minimum mark length (equivalent to 2 T) is 0.154 μm,and then reproduced as the same processes as those of the embodiment 1.

By reproducing a land section L of the information recording medium, asignal having modulated amplitude, equivalent to (I12H−I12L)/I12H, of0.60 can be reproduced. Succeedingly, an error rate of reproduced signalis obtained and resulted in an excellent error rate of 8×10⁻⁶.Consequently, a data without any practical problems can be extracted.Further, an address error rate is about 0.1% at a recorded section, sothat an address data can be restored excellently.

COMPARATIVE EXAMPLE 1

By using the information recording medium 5 of the embodiment 1, it isrecorded and reproduced as the same manner as those of the embodiment 1except for recording on a groove section G.

By reproducing the groove section G of the information recording medium5, a signal having modulated amplitude of 0.38 can be reproduced.Succeedingly, an error rate of reproduced signal is obtained andresulted in an error rate of 4×10⁻³. Consequently, a data, which is toodefective and has many bits being impossible to correct, can beextracted. Further, an address data is completely disordered. Therefore,the address data can not be extracted.

COMPARATIVE EXAMPLE 2

An information recording medium 5 of a comparative example 2 isidentical to that of the embodiment 1 except for a thickness of lighttransmission layer 11, which is assigned to be 0.06 mm. The informationrecording medium 5 of the comparative example 2 is recorded andreproduced as the same manners as those of the embodiment 1.

By reproducing the information recording medium 5, a signal havingmodulated amplitude of 0.46 can be reproduced. However, an eye patternis obscure. Succeedingly, an error rate of reproduced signal is obtainedand resulted in an error rate of 6×10⁻³. Consequently, a data, which istoo defective and has many bits being impossible to correct, can beextracted. Further, the information recording medium 5 is easilyscratched by a test such that the objective lens 50 b is forced tocontact with and to slide on the information recording medium 5.Accordingly, the information recording medium 5 of the comparativeexample 2 is unsuitable for an information recording medium essentially.

COMPARATIVE EXAMPLE 3

An information recording medium of a comparative example 3 is identicalto that of the embodiment 1 except for a thickness of light transmissionlayer 11, which is assigned to be 0.13 mm. The information recordingmedium of the comparative example 3 is recorded and reproduced as thesame manners as those of the embodiment 1.

By reproducing the information recording medium, a signal havingmodulated amplitude of 0.38 can be reproduced. However, an eye patternis obscure. Succeedingly, an error rate of reproduced signal is obtainedand resulted in an error rate of 9×10⁻³. Consequently, a data, which istoo defective and has many bits being impossible to correct, can beextracted. Further, an address error rate is as many as 10% at arecorded section. Consequently, only an address data, which is defectiveand has many bits being impossible to correct, can be extracted.

The information recording medium of the present invention is explainedabove with referring to the embodiments 1 through 5 and the comparativeexamples 1 through 3.

In the present invention, modulated amplitude is assigned to be morethan 0.4 in consideration of that a reproduced signal is added with anoise inherent to a laser when reproducing an information recordingmedium 1. By this assignment, an information recording medium having asignal characteristic, which is compensated for an increased componentof laser noise, is provided.

With respect to a second method of compensating an increased componentof noise inherent to a laser, there is existed a method of regulating areflectivity within a predetermined range. With paying attention to each“reflectivity” of the information recording mediums 1 though 5, resultof a study of “relationship between reflectivity and error rate” isexplained hereafter.

With respect to the information recording medium 5 shown in FIG. 8according to the fifth embodiment of the present invention, severalkinds of information recording mediums are manufactured by varying adepth (height difference between a groove section G and a land sectionL) of the microscopic pattern 20 formed on the substrate 13. Theseinformation recording mediums are reproduced by using the reproducingapparatus 40 composed of the light emitting element 50 a equipped with asemiconductor laser of gallium nitride system compound (its RIN is −125dB/Hz), and a relationship between a reflectivity and an error rate isexamined. Recording is performed under an ideal recording condition fordecreasing an error rate minimally.

A reflectivity can be expressed as an output of reproduced signal. In acase of a phase change material, it is an index correlating tobrightness of a crystalline state. Actually, the information recordingmedium 5 is recorded with a modulated signal, which is the so-called (d,k) code mentioned above. A recording apparatus will be explained later.

Loading the information recording medium 5 into the reproducingapparatus 40 in flat (without declination) and reproducing it obtains areflectivity from a signal having a maximum length used for a code byconnecting a reproduced signal in a DC system outputted form the pickup50 to an oscilloscope. In the case of the 8/16 modulation method usedfor a DVD disc, for example, the maximal length is 14 T. By measuring anI14H as specified by the specification (JIS Standard X6241: 1997), areflectivity is calculated from an absolute reflectivity calibrationline.

Further, an error rate is obtained by measuring a reproduced signalobtained through the demodulator 54.

The result is shown in FIG. 17.

FIG. 17 is a graph exhibiting a relation between a reflectivity and anerror rate.

As shown in FIG. 17, there is existed a distinct relationship between areflectivity and an error rate. It is apparent that an error rateremarkably increases in accordance with a reflectivity decreasing. If apractical error rate is assigned to be 3'10⁻⁴, which is specified for aDVD disc, a necessary reflectivity becomes more than 2%.

Further, the information recording medium 5 may warp by temperaturechange or like in circumstances of utilization of the informationrecording medium 5. Therefore, with assuming that a declination ofapproximate 0.7 degree is possible to occur as a same situation as a DVDdisc, an error rate increases due to coma aberration, which is complexlyproduced by a wavelength λ within a range of 350 to 450 nm, an NA withina range of 0.75 to 0.9 and a thickness of the light transmission layer11 within a range of 0.07 to 0.12 mm.

By the result of measurement, it is found that the error rate of 3×10⁻⁴at the declination of 0.7 degree is equivalent to an error rate of0.7×10⁻⁴ at the declination of zero degree. In other words, the errorrate of 0.7×10⁻⁴ is essential in consideration of a possible declinationwhen using the information recording medium 5 practically. Accordingly,it is understood that a practical reflectivity is more than 5%.

As mentioned above, in the case that a semiconductor laser of galliumnitride system compound is used for a light emitting element, an errorrate can be reduced to a practical level as low as that of the DVD discspecification if a reflectivity of the information recording medium 5 isassigned to be more than 5% in consideration of a noise being added to areproduced signal. Further, it is found by experiments that acorrelation between reflectivity and error rate such as shown in FIG. 17can be obtained as a similar result by using any of the modulationmethods mentioned above.

A maximum mark length can vary by a modulation method. However, a signaloutput almost saturates at more than 6 T by these modulation methods andconverges to a certain value. Consequently, a reflectivity obtained byrecording the information recording medium 1 by the 17PP modulationmethod, for example, and another reflectivity obtained by the 8/16modulation method become a same value as each other.

In consideration of a reproduction characteristic of informationrecording medium, the information recording mediums 1 through 5 of whichreflectivity is assigned to be more than 5% according to the presentinvention are explained hereinbefore.

In consideration of general characteristics of a recording apparatus anda reproducing apparatus, which are equipped with a semiconductor laserof gallium nitride system compound as a light emitting element, andphysical characteristics of the recording layer 12 or 123 composed of aphase change material totally, a practical range of reflectivitynecessary for realizing a total system is explained next.

An output of a semiconductor laser of gallium nitride system compound is30 mW maximally. Generally, an output of light emitting element fallsdown to almost one fifth of original output of the light emittingelement inside a recording apparatus due to a coupling efficiency ofoptical element, which is used for a wavelength λ being within a rangeof 350 to 450 nm. In other words, a laser power becomes 6 mW on eachsurface of the information recording mediums 1 through 5 even though alaser having an output of 30 mW is used. On the contrary, it isdesirable that a recording power is assigned to be higher as high aspossible in order to realize excellent phase change recording incontrast. Therefore, it is necessary for the information recordingmediums 1 through 5 to be recorded by a recording power of about 6 mW.It is necessary for absorptivity and transmissivity of the recordinglayer 12 or 123 of the information recording mediums 1 through 5 to berelatively higher value therefor.

Noise of a semiconductor laser of gallium nitride system compound andincreasing of noise of a reproducing apparatus equipped with such asemiconductor laser are explained hereinbefore. However, it is necessaryto pay attention to that noise depends upon a reproduction power. When alaser noise is measured by varying a reproduction power, it is foundthat noise increases in a lower laser power by using a semiconductorlaser of gallium nitride system compound, particularly, it is found thatthere is existed a critical point at the reproduction power of 0.35 mWon a surface of information recording medium. In other words, if areproduction power is below 0.35 mW, noise increases remarkably.Therefore, it is necessary for a reproduction power of the informationrecording mediums 1 through 5 to be more than 0.35 mW.

With respect to physical characteristics of the recording layer 12 or123, if a reproduction power is increased, the recording layer isthermally damaged and there is existed a phenomenon such that a recordmark M disappears. Particularly, in a case that a wavelength λ is withinthe range of 350 to 450 nm, energy density of a spot S to be formed onan information recording medium becomes larger than that of a redsemiconductor laser (of which wavelength λ is within a range of 635 to830 nm, for example). Therefore, a reproduction power is assigned to belower. However, since a minimum reproduction power is limited asmentioned above, a permitted limit of reproduction power is obliged tobe narrower. In order to increase resistivity for reproduction power,that is, in order to assign a reproduction power to be higher, it isnecessary for absorptivity and transmissivity of the recording layer 12or 123 of the information recording mediums 1 through 5 to be relativelylower value.

In consideration of general characteristics of a recording apparatus anda reproducing apparatus, which are equipped with a semiconductor laserof gallium nitride system compound as a light emitting element, andphysical characteristics of the recording layer 12 or 123 composed of aphase change material totally, as mentioned above, a recording power isassumed to be about 6 mW and a reproduction power is necessary to bemore than 0.35 mW. Further, an information recording medium of whichrecord mark M on the recording layer 12 or 123 is hardly erased by thereproduction power of more than 0.35 mW is required. In order to satisfythese various limits, it is necessary for absorptivity andtransmissivity of the recording layer 12 or 123 of the informationrecording mediums 1 through 5 to be relatively higher value with respectto a material for the recording layer 12 or 123 of the informationrecording mediums 1 through 5 due to limitation for recording power.Furthermore, it is necessary for the absorptivity and transmissivity tobe relatively a lower value due to limitation of resistivity forreproduction power.

In other words, it is necessary for absorptivity and transmissivity tobe set within a predetermined range. A total amount of absorptivity,transmissivity and reflectivity is one. Therefore, it is also necessaryfor the reflectivity to be set within a predetermined range.

A range of reflectivity satisfying the above-mentioned various limits isexperimentally studied and a range of 12 to 26% is found. Processes ofexperimental study are definitely explained as embodiments 6 through 12and comparative examples 4 and 5 herein after.

Embodiments 6 through 12

FIG. 18 is a table showing reflectivity and reproduction characteristicsof embodiments 6 through 12 and comparative examples 4 and 5.

Polycarbonate having a thickness of 1.1 mm is used for a substrate 13 ofa phase change type information recording medium 5. Further, theinformation recording medium 5 is manufactured by using materials suchas Ag₉₈Pd₁Cu₁ for a reflective layer 121, ZnS—SiO₂ (in the proportion of80:20 in mol %) for a first protective layer 122, Ge₈Sb₆₉Te₂₃ for arecording layer 123 and ZnS—SiO₂ (in the proportion of 80:20 in mol %)for a second protective layer 124, wherein each layer is formed in acertain film thickness shown in FIG. 18. Finally, polycarbonate having athickness of 0.10 mm is laminated on the second protective layer 124 asa light transmission layer 11. Consequently, the information recordingmedium 5 is completed.

An address data is recorded in a wobbling shape on a land section L ofthe information recording medium 5 by the frequency modulation method,wherein a phase having a phase difference of ±π/2.5 is selected so asfor a wave to be continuous at a point of changing a frequency.

The information recording medium 5 is designed with assuming that it isrecorded by using a light beam having a wavelength λ of 405 nm and anobjective lens having a numerical aperture NA of 0.85, and a pitch Pbetween land sections L is 0.32 μm. The reflective layer 121 andrecording layer 123 are formed in an atmosphere of 5 mTorr of argon gasby the DC sputtering, wherein a vacuum chamber used for sputtering ispreviously evacuated as low as less than 1×10⁻⁶ Torr.

Further, the completed information recording medium 5 is initializedsuch that the recording layer 123 is changed in phase from an amorphousstate low in reflectivity to a crystalline state high in reflectivity byirradiating a laser beam from the light transmission layer 11 side.

The information recording medium 5 is loaded into a recording apparatuscomposed of a pickup having a wavelength A of 405 nm and a numericalaperture NA of 0.85, and a recording signal is recorded on a landsection L by a modulated signal, which is modulated by the 17PPmodulation method, wherein a minimum mark length (equivalent to 2 T) is0.160 μm. Conditions for recording are as follows: 6.0 mW of recordingpower, 2.6 mW of bias power, 0.1 mW of bottom power between multi-pulsesand bottom power of cooling pulse, and 5.3 m/s of linear velocity.

Further, recording is a so-called recording by multi-pulses method,which adopts a three-value power modulation such that each width of ahead pulse and a succeeding pulse is 0.4 times the recording period 1 Tand a width of cooling pulse is 0.4 times the recording period 1 T.

The information recording medium 5 recorded with the above-mentionedrecording signal is loaded into the reproducing apparatus 40 equippedwith the pickup 50 having the wavelength λ of 405 nm and the numericalaperture NA of 0.85 shown in FIG. 15. Items to be evaluated are asfollows: reflectivity, modulated amplitude, equivalent to (I8H−I8L)/I8H,reproduction laser power at limit of deterioration, reproduction errorrate of record mark M and address error rate. The reproduction laserpower at limit of deterioration is obtained by measuring a power suchthat reproducing the information recording medium 5 at the reproductionpower of 0.3 mW first, increasing the reproduction power from 0.3 mWgradually, and measure a power when it is recognized that reproductionis deteriorated. The reproduction laser power at limit of deterioration,reproduction error rate and address error rate out of the items to beevaluated are judged by a reference value and determined to beacceptable or not.

With respect to a standard for judging the reproduction laser power atlimit of deterioration, one can be reproduced by the reproduction powerof more than 0.35 mW is acceptable (◯) and another can not be reproducedis not acceptable (×). With respect to a standard for judging thereproduction error rate, one can be reproduced by the error rate of lessthan 0.7×10⁻⁴ is acceptable (◯) and another can not be reproduced is notacceptable (×). Further, with respect to a standard for judging theaddress error rate, one can be reproduced by the error rate of less than5% (it is a limit of restoration by an error correction) is acceptable(◯) and another can not be reproduced is not acceptable (×). Actualvalues of reflectivity, modulated amplitude and reproduction laser powerat limit of deterioration, and judgment result of reproduction laserpower at limit of deterioration, reproduction error rate and addresserror rate are summarized in FIG. 18. In FIG. 18, “Emb.” and “Comp.”represent “Embodiment” and “comparative example” respectively.

As shown in FIG. 18, each information recording medium 5 manufactured byhaving a reflectivity within a range of 12 to 26% according to theembodiments 6 through 12 is excellent in deteriorated reproduction,reproduction error rate and address error rate. Consequently, theinformation recording medium according to the embodiments 6 through 12can satisfy performance as a total system.

COMPARATIVE EXAMPLE 4

An information recording medium of which each layer is altered so as fora reflectivity to be 11.0% is prepared for the information recordingmedium 5 according to the comparative example 4 and evaluated as thesame manner as mentioned above in the embodiments 6 through 12. A resultof evaluation is listed in FIG. 18.

According to the information recording medium 5 of the comparativeexample 4, reproduction is deteriorated at the reproduction power of0.34 mW. Therefore, it is judged that sensitivity of the recording layer123 is too high. Accordingly, an information recording medium having areflectivity of less than 11% is not suitable for a total system.

COMPARATIVE EXAMPLE 5

An information recording medium of which each layer is altered so as fora reflectivity to be 28.2% is prepared for the information recordingmedium 5 according to the comparative example 5 and evaluated as thesame manner as mentioned above in the embodiments 6 through 12. A resultof evaluation is listed in FIG. 18.

In a case of the comparative example 5, there is not existed a problemof deteriorated reproduction. However, the reproduction error rate ishigh and resulted in defective. It is supposed to be a cause that themodulated amplitude is too small as low as 0.389. In other words, it issupposed that sensitivity of the recording layer 123 is too low to berecorded in sufficient contrast. Therefore, an information recordingmedium having a reflectivity of more than 28% is not suitable for atotal system.

According to the evaluation result of the embodiments 6 through 12 andthe comparative examples 4 and 5, it is understood that a range ofreflectivity suitable for a total system is 12 to 26%.

With referring to FIG. 17, the embodiments 6 through 12, the comparativeexamples 4 and 5 and FIG. 18, the information recording mediums 1through 5 are explained hereinbefore. According to the presentinvention, in consideration of that noise inherent to a laser is addedto a reproduced signal while reproducing the information recordingmedium 1, the reflectivity is assigned to be more than 5%, preferably tobe within a range of 12 to 26%. Accordingly, an information recordingmedium having a signal characteristic of compensating an increasedcomponent caused by laser noise is provided.

The reproducing apparatus 40 shown in FIG. 15 of the present inventionand the information recording mediums 1 through 5 of the presentinvention, which are loaded therein, are explained above. The firstreproduction apparatus 40 explained hereinbefore is a reproducingapparatus for reading out information recorded in the recording layer 12or 123, particularly, can reproduce contents recorded continuously for along period of time. For example, it can be used for reproducing a HDTV(high definition television) program and a movie recorded by videoequipment.

With referring to FIG. 19, a second reproducing apparatus 41 accordingto the present invention is explained next.

A case of using the information recording medium 1 as for an informationrecording medium is explained hereinafter. However, the otherinformation recording mediums 2 through 5 is the same situation as theinformation recording medium 1.

The second reproducing apparatus 41 is identical to the firstreproducing apparatus 40 shown in FIG. 15 except for being equipped withan auxiliary information demodulator 56 allocated between the pickup 50and the controller 60, wherein an auxiliary information is read out by apickup 50. It is a reproducing apparatus used for index reproducing aHDTV program and a movie in video recording and for index reproducing acomputer recorded with data.

As mentioned above, a signal transmitted from the pickup 50 and to thedemodulator 54 is a total sum signal (that is, Ia+Ib+Ic+Id) of outputfrom all 4 sections of a 4-division light detector not shown, whereineach of Ia, Ib, Ic and Id corresponds to each output of a 4-divisionlight detector for a DVD disc defined by the JIS Standard No. X6241:1997. On the other hand, another signal transmitted from the pickup 50to the auxiliary information demodulator 56 is a differential signal(that is, “(Ia−Ib)−(Ic−Id)”) of output from the 4-division lightdetector in the radial direction. An auxiliary information recorded in ashape of wobbling groove on the information recording medium 1 can beextracted by monitoring the differential signal because the wobbling isformed in the radial direction.

With respect to an actual configuration of the auxiliary informationdemodulator 56, it is composed of at least one of an amplitudemodulation (AM) demodulator, a frequency modulation (FM) demodulator anda phase modulation (PM) demodulator. In a case of the AM demodulator, anenvelope detector circuit can be suitably used. In a case of the FMdemodulator, a frequency detector circuit and a synchronous detectorcircuit can be suitably used. In a case of the PM detector, asynchronous detector circuit, a delay detector circuit and an envelopedetector circuit can be suitably used. A sum signal may leak in adifferential signal in the radial direction although it is quite little.In order to avoid such leakage, a band pass filter tuned in a frequencyband of the auxiliary information can be connected in front of theauxiliary information demodulator 56.

Operations of the second reproducing apparatus 41 are explained next.

A reproducing light 70 is emitted from a light emitting element 50 a ofthe pickup 50 and converged at the microscopic pattern 20 in theinformation recording medium 1. Actually, the reproducing light 70 isfocused on the microscopic pattern 20, which is allocated at a depth of0.07 to 0.12 mm equivalent to a thickness of the light transmissionlayer 11. Succeedingly, tracking of the reproducing light 70 isperformed to either one of the groove section G or the land section L.The tracking is performed with choosing a predetermined side. However,as mentioned above, choosing the land section L is most desirable.

Then, an auxiliary information is read out by transmitting thedifferential signal (“(Ia+Ib)−(Ic+Id)”) in the radial direction from thepickup 50 to the auxiliary information demodulator 56. At this moment,with paying attention to an address information out of various kinds ofauxiliary information, the auxiliary information is compared with anaddress for indexing a data inputted to a controller 60.

If the auxiliary information does not coincide with the address, thecontroller 60 sends a signal to a servo device 52 and directs to search.Searching is performed such that a number of rotations of a motor 51 isreset to a number of rotations, which is suitable for a radius betweenthe motor 51 and the pickup 50, according to movement in the radialdirection of the pickup 50 while scanning the movement of the pickup 50in the radial direction. During a process of scanning, an addressoutputted from the auxiliary information demodulator 56, which receivesa differential signal from the pickup 50, is compared with a certainaddress. The searching is continued until they coincide with each other.When they coincide, scanning in the radial direction is interrupted andreproduction is switched over to continuous reproduction. An output fromthe demodulator 54, which is inputted with the sum signal (Ia+Ib+Ic+Id),becomes a signal of a demodulated data stream obtained by indexing andis inputted to an interface (I/F) 55. Finally, a signal is outputtedexternally in accordance with controlling by the controller 60.

As mentioned above, the information recording medium 1 and the secondreproducing apparatus 41 according to the present invention are designedfor coping with the reproducing light 70, which is produced by the lightemitting element 50 a having single wavelength λ within the range of 350to 450 nm and the objective lens 50 b having the numerical aperture NAof 0.75 to 0.9. Therefore, the second reproducing apparatus canpreferably reproduce an auxiliary information and perform indexreproduction of a data stream in conjunction with reproducing theinformation recording medium 1 preferably.

With referring to FIG. 20, a recording apparatus 90 according to thepresent invention is explained, wherein the information recording medium1 is used as an information recording medium for explaining functionsand operations of the recording apparatus 90. However, the otherinformation recording mediums 2 through 5 are the same situations as theinformation recording medium 1.

FIG. 20 is a block diagram of a recording apparatus according to thepresent invention.

As shown in FIG. 20, the recording apparatus 90 is similar to the secondreproducing apparatus 41 shown in FIG. 19 except for that thedemodulator 54 is replaced with a modulator 82 for modulating anoriginal data and a waveform converter 83 for transforming a modulatedsignal from the modulator 82 into a form suitable for recording on theinformation recording medium 1, which are connected in series. Furtherthe I/F 55 is replaced with an interface (I/F) 81 for receiving anexternal signal to be recorded.

The recording apparatus 90 is an apparatus for recording a computerdata, for example, at a predetermined address newly or recording a HDTVprogram or a movie continuously from a predetermined address as a videorecording.

The modulator 82 is a modulator of converting an 8-bit original datainto 16 bits, in the case of the 8/16 modulation (EFM plus) method for aDVD disc. The waveform converter 82 transforms a modulated signalreceived from the modulator 82 into a form suitable for recording on theinformation recording medium 1. Actually, the waveform converter 83 is aconverter, which converts the modulated signal into a recording pulsesatisfying a recording characteristic of the recording layer 12 of theinformation recording medium 1. For example, in a case that therecording layer 12 is composed of a phase change material, a so-calledmulti-pulse is formed. In other words, the modulated signal is dividedinto a unit of a channel bit or less and power is changed into arectangular waveform, wherein peak power, bottom power erase power and apulse time duration constituting a multi-pulse are assigned inaccordance with a direction of a controller 60.

Operations of the recording apparatus 90 are explained next.

A reproducing light 70 is emitted from a light emitting element 50 a ofa pickup 50 and converged at the microscopic pattern 20 in theinformation recording medium 1. Actually, the reproducing light 70 isfocused on the microscopic pattern 20, which is allocated at a depth of0.07 to 0.12 mm equivalent to a thickness of the light transmissionlayer 11. Succeedingly, tracking of the reproducing light 70 isperformed to either one of the groove section G or the land section L.The tracking is performed with choosing a predetermined side. However,as mentioned above, choosing the land section L is most desirable. Then,an auxiliary information is read out by transmitting the differentialsignal (“(Ia+Ib)−(Ic+Id)”) in the radial direction from the pickup 50 toan auxiliary information demodulator 56.

At this moment, with paying attention to an address information out ofvarious kinds of auxiliary information, the auxiliary information iscompared with an address for indexing a data inputted to the controller60. If the auxiliary information does not coincide with the address, thecontroller 60 sends a signal to a servo device 52 and directs to search.Searching is performed such that a number of rotations of a motor 51 isreset to a number of rotations, which is suitable for a radius betweenthe motor 51 and the pickup 50, according to movement in the radialdirection of the pickup 50 while scanning the movement of the pickup 50in the radial direction.

During a process of scanning, an address outputted from the auxiliaryinformation demodulator 56, which receives a differential signal fromthe pickup 50, is compared with a certain address. The searching iscontinued until they coincide with each other. When they coincide,scanning in the radial direction is interrupted and reproduction isswitched over to continuous reproduction. In other words, a datainputted from the I/F 81 is modulated by the modulator 82 in accordancewith controlling by the controller 60. Succeedingly, the data modulatedby controlling of the controller 60 is inputted to the waveformconverter 83 and converted into a format suitable for recording, andthen outputted to a pickup 50.

In the pickup 50, a recording light 80 of which a recording power isaltered to that assigned by the waveform converter 83 is generated andirradiated on the information recording medium 1. Consequently,recording at a predetermined address on the information recording medium1 is performed. It is possible that the differential signal(“(Ia+Ib)−(Ic+Id)”) in the radial direction is read out by the recordinglight 80, and an address can be extracted from the auxiliary informationdemodulator 56 even while recording. Therefore, a regional recordinglimited as far as an address desired by a user can be realized.

As mentioned above, the information recording medium 1 and the recordingapparatus 90 according to the present invention are designed for copingwith the reproducing light 70 and the recording light 80, which aregenerated by the light emitting element 50 a having single wavelength λwithin the range of 350 to 450 nm and an objective lens 50 b having thenumerical aperture NA of 0.75 to 0.9. Therefore, the recording apparatus90 can preferably record on the information recording medium 1 and, atthe same time can reproduce an auxiliary information, and then performrandom indexing for recording.

The information recording mediums 1 through 5, the first and secondreproducing apparatuses 40 and 41 and the recording apparatus 90 areexplained in details hereinbefore. Further, in the embodiments of thepresent invention, fundamental areas of the present invention areexplained. However, it is apparent that many changes, modifications andvariations in the arrangement of equipment and devices and in materialswithout departing from the invention concept disclosed herein. Forexample, an information recording medium having multi-layers (forinstance, triple and quadruple layers) of a set of the recording layer 7and the light transmission layer 8 laminated together can be applicableother than the information recording medium 1 having a single layer anddouble layers of the microscopic pattern 20.

Furthermore, with respect to the first and second reproducing apparatus40 and 41 and the recording apparatus 90, it is also apparent that eachoperation of them is not limited to those mentioned above withoutdeparting the invention concept disclosed herein. For example, areproducing method and a recording method, which derive from replacingeach operation of the first and second reproducing apparatuses 40 and 41and the recording apparatus 90 with each step of reproducing andrecording processes, can be introduced for the present invention.Moreover, it is apparent that a computer program, which performs eachstep of the reproducing method, and another computer program, whichperforms each step of the reproducing method, are included in thepresent invention.

Effect of the Invention

As mentioned above, according to an aspect of the present invention,there provided an information recording medium, which is at leastcomposed of a substrate having a microscopic pattern constituted by ashape of continuous substance of approximately parallel grooves formedwith a groove section and a land section alternately, a recording layerformed on the microscopic pattern and a light transmission layer formedon the recording layer. Further, the microscopic pattern is formed withhaving a relation of P<λ/NA and a thickness of the light transmissionlayer is within a range of 0.07 to 0.12 mm, wherein P is a pitch of thegroove section or the land section, λ is a wavelength of reproducinglight beam and NA is a numerical aperture of objective lens. Therefore,an information recording medium, which can reduce cross erase and alsobe recorded in higher density, can be obtained. Furthermore, recordingin accordance with difference of reflectivity or phase difference isperformed by assigning modulated amplitude to be more than 0.4, so thatan error rate can be decreased to a practical level.

According to another aspect of the present invention, there provided areproducing apparatus for reproducing an information recording medium,which is composed of a substrate having a microscopic patternconstituted by a shape of continuous substance of approximately parallelgrooves formed with a groove section and a land section alternately. Thereproducing apparatus is at least composed of a light emitting elementof which a wavelength of reproducing light is λ nm, and having RIN(relative intensity noise) of less than −125 dB/Hz and an objective lenshaving a numerical aperture NA. Further, the λ is within a range of 350to 450 nm and the NA is within a range of 0.75 to 0.9. Furthermore, thereproducing light is irradiated on either one of the land section andthe groove section. Therefore, cross erase can be reduced.

In the information recording medium according to the present invention,an auxiliary information such as an address data is recorded in shape ona part of or all over the microscopic pattern by an amplitude modulation(AM) method, so that an information can be demodulated even in a low C/N(carrier to noise ratio) circumstance. Further, an auxiliary informationsuch as an address data is recorded in shape on a part of or all overthe microscopic pattern by a frequency modulation (FM) method, so thatan information can be demodulated by a simplified circuit. Particularly,by using the FM method selected with a proper phase, which is suitablefor two waves to be connected continuously at a point where theirfrequencies change over, a reproduction envelope becomes approximatelyconstant and stable reproduction can be realized. Furthermore, anauxiliary information such as an address data is recorded in shape on apart of or all over the microscopic pattern by a phase modulation (PM)method, so that an information can be demodulated by a synchronousdetection even in a low C/N circumstance. In particular, if phasedifference between a high frequency component and a low frequencycomponent is assigned to be ±π/2.5, excellent signal demodulation can berealized by the synchronous detection even in a low C/N circumstance.

In addition thereto, an auxiliary information such as an address datacan be improved in stability of readout, if the auxiliary information ispreviously formed in a data modulated in a base-band, in which a numberof same bits continuing is limited to be less than a predeterminedquantity.

It should be understood that many modifications and adaptations of theinvention will become apparent to those skilled in the art and it isintended to encompass such obvious modifications and changes in thescope of the claims appended hereto.

1. An information recording medium comprising: a substrate having amicroscopic pattern, having a continuous shape of approximately parallelgrooves formed with alternating groove and land sections; a recordinglayer formed on the microscopic pattern; a light transmission layerformed on the recording layer, wherein the recording layer is formed bya phase change material; and wherein the microscopic pattern is formedso as to satisfy a relation of P<λ/NA and a thickness of the lighttransmission layer is within a range of 0.07 to 0.12 mm, wherein P is apitch of the groove section or the land section, λ is a wavelength ofreproducing light beam and NA is a numerical aperture of an objectivelens; and wherein the land section is wobbled in the radial directionand having a wobbled shape corresponding to a signal to be recorded onthe land section resulting from the modulation of a phase modulated wavethat is further modulated by a single frequency wave, the singlefrequency wave having a frequency of integral multiples or one overintegral multiples of a frequency of the phase modulated wave, andwherein the frequency of the single frequency wave is different fromthat of the phase modulated wave.
 2. A recording apparatus comprising: arecording medium having (a) a substrate having a microscopic pattern,having a continuous shape of approximately parallel grooves formed withalternating groove and land sections; (b) a recording layer formed onthe microscopic pattern; (c) a light transmission layer formed on therecording layer; wherein the microscopic pattern is formed so as tosatisfy a relation of P<λ/NA and a thickness of the light transmissionlayer is within a range of 0.07 to 0.12 mm, and wherein P is a pitch ofthe groove section or the land section, λ is a wavelength of reproducinglight beam and NA is a numerical aperture of an objective lens; andwherein the land section is wobbled in the radial direction and having awobbled shape corresponding to a signal to be recorded on the landsection resulting from the modulation of a phase modulated wave that isfurther modulated by a single frequency wave, the single frequency wavehaving a frequency of integral multiples or one over integral multiplesof a frequency of the phase modulated wave, and wherein the frequency ofthe single frequency wave is different from that of the phase modulatedwave; the recording apparatus further comprising: (d) a pickup composedof a light emitting element having a wavelength of λ within a range of350 to 450 nm and an objective lens having a numerical aperture of NAwithin a range of 0.75 to 0.9 for reading out reflected light from andrecording on the information recording medium; (e) a motor for rotatingthe information recording medium; (f) servo means for controlling thedrive of the pickup and the motor; (g) a turntable for supporting theinformation recording medium while rotating; (h) interface (I/F) meansfor receiving the original information signal; (i) modulator means formodulating the original information signal; (j) waveform converter meansfor converting the original information signal into a format suitablefor a recording characteristic of the recording layer of the informationrecording medium; (k) auxiliary information demodulator means fordemodulating a differential signal outputted from the pickup; and (l)controlling means for controlling the entire recording apparatus.